diff --git a/docs/src/api-print.md b/docs/src/api-print.md
index 970a5f72..2b0e2dc3 100644
--- a/docs/src/api-print.md
+++ b/docs/src/api-print.md
@@ -42,7 +42,7 @@ ocp = Model()
 
 state!(ocp, 2, "x", ["r", "v"]) # dimension of the state with the names of the components
 control!(ocp, 1)           # dimension of the control
-time!(ocp, [0, 1], "s")    # initial and final time, with the name of the variable time
+time!(ocp, t0=0, tf=1, name="s")    # initial and final time, with the name of the variable time
 
 constraint!(ocp, :initial, lb=[-1, 0], ub=[-1, 0])
 constraint!(ocp, :final  , lb=[ 0, 0], ub=[ 0, 0])
diff --git a/src/model.jl b/src/model.jl
index 2a7f5862..30bbbc45 100644
--- a/src/model.jl
+++ b/src/model.jl
@@ -340,7 +340,9 @@ end
 """
 $(TYPEDSIGNATURES)
 
-Fix initial time, final time is free and given by the variable at the provided index.
+Set the initial and final times. We denote by t0 the initial time and tf the final time.
+The optimal control problem is denoted ocp.
+When a time is free, then one must provide the corresponding index of the ocp variable.
 
 !!! note
 
@@ -349,166 +351,88 @@ Fix initial time, final time is free and given by the variable at the provided i
 # Examples
 
 ```jldoctest
-julia> time!(ocp, 0, Index(2), "t")
+julia> time!(ocp, t0=0,   tf=1  ) # Fixed t0 and fixed tf
+julia> time!(ocp, t0=0,   indf=2) # Fixed t0 and free  tf
+julia> time!(ocp, ind0=2, tf=1  ) # Free  t0 and fixed tf
+julia> time!(ocp, ind0=2, indf=3) # Free  t0 and free  tf
 ```
-"""
-function time!(ocp::OptimalControlModel{<: TimeDependence, NonFixed}, t0::Time, indf::Index, name::String=__time_name())
-    __check_variable_set(ocp)
-    __is_time_set(ocp) && throw(UnauthorizedCall("the time has already been set. Use time! once."))
-    (indf.val > ocp.variable_dimension) && throw(IncorrectArgument("out of range index of variable"))
-    #
-    ocp.initial_time = t0
-    ocp.final_time = indf
-    ocp.time_name = name
-    ocp.initial_time_name = t0 isa Integer ? string(t0) : string(round(t0, digits=2))
-    ocp.final_time_name = ocp.variable_components_names[indf]
-    nothing # to force to return nothing
-end
-
-function time!(ocp::OptimalControlModel, t0::Time, indf::Index, name::Symbol)
-    time!(ocp, t0, indf, string(name))
-end
-
-"""
-$(TYPEDSIGNATURES)
 
-Fix final time, initial time is free and given by the variable at the provided index.
+When you plot a solution of an optimal control problem, the name of the time variable appears.
+By default, the name is "t".
+Consider you want to set the name of the time variable to "s".
 
-# Examples
 ```jldoctest
-julia> time!(ocp, Index(2), 1, "t")
+julia> time!(ocp, t0=0, tf=1, name="s") # name is a String
+# or
+julia> time!(ocp, t0=0, tf=1, name=:s ) # name is a Symbol  
 ```
 """
-function time!(ocp::OptimalControlModel{<: TimeDependence, NonFixed}, ind0::Index, tf::Time, name::String=__time_name())
-    __check_variable_set(ocp)
-    __is_time_set(ocp) && throw(UnauthorizedCall("the time has already been set. Use time! once."))
-    (ind0.val > ocp.variable_dimension) && throw(IncorrectArgument("out of range index of variable"))
-    ocp.initial_time = ind0
-    ocp.final_time = tf
-    ocp.time_name = name
-    ocp.initial_time_name = ocp.variable_components_names[ind0]
-    ocp.final_time_name = tf isa Integer ? string(tf) : string(round(tf, digits=2))
-    nothing # to force to return nothing
-end
-
-function time!(ocp::OptimalControlModel, ind0::Index, tf::Time, name::Symbol)
-    time!(ocp, ind0, tf, string(name))
-end
+function time!(
+    ocp::OptimalControlModel{<: TimeDependence, VT};
+    t0::Union{Time, Nothing}=nothing,
+    tf::Union{Time, Nothing}=nothing,
+    ind0::Union{Integer, Nothing}=nothing, 
+    indf::Union{Integer, Nothing}=nothing, 
+    name::Union{String, Symbol}=__time_name()) where VT
 
-"""
-$(TYPEDSIGNATURES)
+    # check if the problem has been set to Variable or NonVariable
+    VT == NonFixed && (!isnothing(ind0) || !isnothing(indf)) && __check_variable_set(ocp)
 
-Initial and final times are free and given by the variable at the provided indices.
+    # check if indices are in 1:q
+    q = ocp.variable_dimension
+    !isnothing(ind0) && !(1 ≤ ind0 ≤ q) && throw(IncorrectArgument("the index of t0 variable must be contained in 1:$q"))
+    !isnothing(indf) && !(1 ≤ indf ≤ q) && throw(IncorrectArgument("the index of tf variable must be contained in 1:$q"))
 
-# Examples
-```jldoctest
-julia> time!(ocp, Index(2), Index(3), "t")
-```
-"""
-function time!(ocp::OptimalControlModel{<: TimeDependence, NonFixed}, ind0::Index, indf::Index, name::String=__time_name())
-    __check_variable_set(ocp)
+    # check if the function has been already called
     __is_time_set(ocp) && throw(UnauthorizedCall("the time has already been set. Use time! once."))
-    (ind0.val > ocp.variable_dimension) && throw(IncorrectArgument("out of range index of variable"))
-    (indf.val > ocp.variable_dimension) && throw(IncorrectArgument("out of range index of variable"))
-    ocp.initial_time = ind0
-    ocp.final_time = indf
-    ocp.time_name = name
-    ocp.initial_time_name = ocp.variable_components_names[ind0]
-    ocp.final_time_name = ocp.variable_components_names[indf]
-    nothing # to force to return nothing
-end
-
-function time!(ocp::OptimalControlModel, ind0::Index, indf::Index, name::Symbol)
-    time!(ocp, ind0, indf, string(name))
-end
-
-"""
-$(TYPEDSIGNATURES)
-
-Fix initial and final times to `times[1]` and `times[2]`, respectively.
-
-# Examples
-
-```jldoctest
-julia> time!(ocp, [ 0, 1 ])
-julia> ocp.initial_time
-0
-julia> ocp.final_time
-1
-julia> ocp.time_name
-"t"
-
-julia> time!(ocp, [ 0, 1 ], "s")
-julia> ocp.initial_time
-0
-julia> ocp.final_time
-1
-julia> ocp.time_name
-"s"
-
-julia> time!(ocp, [ 0, 1 ], :s)
-julia> ocp.initial_time
-0
-julia> ocp.final_time
-1
-julia> ocp.time_name
-"s"
-```
-"""
-function time!(ocp::OptimalControlModel, times::Times, name::String=__time_name())
-    (length(times) != 2) && throw(IncorrectArgument("times must be of dimension 2"))
-    time!(ocp, times[1], times[2], name)
-end
-
-function time!(ocp::OptimalControlModel, times::Times, name::Symbol)
-    time!(ocp, times, string(name))
-end
-
-"""
-$(TYPEDSIGNATURES)
 
-Fix initial and final times to `times[1]` and `times[2]`, respectively.
+    # check consistency
+    !isnothing(t0) && !isnothing(ind0) && throw(IncorrectArgument("Providing t0 and ind0 has no sense. The initial time cannot be fixed and free."))
+     isnothing(t0) &&  isnothing(ind0) && throw(IncorrectArgument("Please either provide the value of the initial time t0 (if fixed) or its index in the variable of ocp (if free)."))
+    !isnothing(tf) && !isnothing(indf) && throw(IncorrectArgument("Providing tf and indf has no sense. The final time cannot be fixed and free."))
+     isnothing(tf) &&  isnothing(indf) && throw(IncorrectArgument("Please either provide the value of the final time tf (if fixed) or its index in the variable of ocp (if free)."))
 
-# Examples
+    VT == Fixed && !isnothing(ind0) && throw(IncorrectArgument("You cannot have the initial time free (ind0 is provided) and the ocp non variable."))
+    VT == Fixed && !isnothing(indf) && throw(IncorrectArgument("You cannot have the final time free (indf is provided) and the ocp non variable."))
 
-```jldoctest
-julia> time!(ocp, 0, 1)
-julia> ocp.initial_time
-0
-julia> ocp.final_time
-1
-julia> ocp.time_name
-"t"
+    #
+    name = name isa String ? name : string(name)
 
-julia> time!(ocp, 0, 1, "s")
-julia> ocp.initial_time
-0
-julia> ocp.final_time
-1
-julia> ocp.time_name
-"s"
+    # core
+    @match (t0, ind0, tf, indf) begin
+        (::Time, ::Nothing, ::Time, ::Nothing) => begin # (t0, tf)
+            ocp.initial_time      = t0
+            ocp.final_time        = tf
+            ocp.time_name         = name
+            ocp.initial_time_name = t0 isa Integer ? string(t0) : string(round(t0, digits=2))
+            ocp.final_time_name   = tf isa Integer ? string(tf) : string(round(tf, digits=2))
+        end
+        (::Nothing, ::Integer, ::Time, ::Nothing) => begin # (ind0, tf)
+            ocp.initial_time      = Index(ind0)
+            ocp.final_time        = tf
+            ocp.time_name         = name
+            ocp.initial_time_name = ocp.variable_components_names[ind0]
+            ocp.final_time_name   = tf isa Integer ? string(tf) : string(round(tf, digits=2))
+        end
+        (::Time, ::Nothing, ::Nothing, ::Integer) => begin # (t0, indf)
+            ocp.initial_time      = t0
+            ocp.final_time        = Index(indf)
+            ocp.time_name         = name
+            ocp.initial_time_name = t0 isa Integer ? string(t0) : string(round(t0, digits=2))
+            ocp.final_time_name   = ocp.variable_components_names[indf]
+        end
+        (::Nothing, ::Integer, ::Nothing, ::Integer) => begin # (ind0, indf)
+            ocp.initial_time      = Index(ind0)
+            ocp.final_time        = Index(indf)
+            ocp.time_name         = name
+            ocp.initial_time_name = ocp.variable_components_names[ind0]
+            ocp.final_time_name   = ocp.variable_components_names[indf]
+        end
+        _ => throw(IncorrectArgument("Provided arguments are inconsistent."))
+    end 
 
-julia> time!(ocp, 0, 1, :s)
-julia> ocp.initial_time
-0
-julia> ocp.final_time
-1
-julia> ocp.time_name
-"s"
-```
-"""
-function time!(ocp::OptimalControlModel, t0::Time, tf::Time, name::String=__time_name())
-    __is_time_set(ocp) && throw(UnauthorizedCall("the time has already been set. Use time! once."))
-    ocp.initial_time=t0
-    ocp.final_time=tf
-    ocp.time_name = name
-    ocp.initial_time_name = t0 isa Integer ? string(t0) : string(round(t0, digits=2))
-    ocp.final_time_name = tf isa Integer ? string(tf) : string(round(tf, digits=2))
     nothing # to force to return nothing
-end
 
-function time!(ocp::OptimalControlModel, t0::Time, tf::Time, name::Symbol)
-    time!(ocp, t0, tf, string(name))
 end
 
 """
diff --git a/src/onepass.jl b/src/onepass.jl
index 37cf35d1..f099d8c7 100644
--- a/src/onepass.jl
+++ b/src/onepass.jl
@@ -198,26 +198,26 @@ p_time!(p, ocp, t, t0, tf; log=false) = begin
     p.tf = tf
     tt = QuoteNode(t)
     code = @match (has(t0, p.v), has(tf, p.v)) begin
-        (false, false) => :( time!($ocp, $t0, $tf, $tt) )
+        (false, false) => :( time!($ocp; t0=$t0, tf=$tf, name=$tt) )
         (true , false) => @match t0 begin
-            :( $v1[$i] ) && if (v1 == p.v) end => :( time!($ocp, Index($i), $tf, $tt) )
+            :( $v1[$i] ) && if (v1 == p.v) end => :( time!($ocp; ind0=$i, tf=$tf, name=$tt) )
             :( $v1     ) && if (v1 == p.v) end => quote
                 ($ocp.variable_dimension ≠ 1) &&
 		        throw(IncorrectArgument("variable must be of dimension one for a time"))
-                time!($ocp, Index(1), $tf, $tt) end
+                time!($ocp; ind0=1, tf=$tf, name=$tt) end
             _                                  =>
 	            return __throw("bad time declaration", p.lnum, p.line) end
         (false, true ) => @match tf begin
-            :( $v1[$i] ) && if (v1 == p.v) end => :( time!($ocp, $t0, Index($i), $tt) )
+            :( $v1[$i] ) && if (v1 == p.v) end => :( time!($ocp; t0=$t0, indf=$i, name=$tt) )
             :( $v1     ) && if (v1 == p.v) end => quote
                 ($ocp.variable_dimension ≠ 1) &&
 		        throw(IncorrectArgument("variable must be of dimension one for a time"))
-                time!($ocp, $t0, Index(1), $tt) end
+                time!($ocp; t0=$t0, indf=1, name=$tt) end
             _                                  =>
 	            return __throw("bad time declaration", p.lnum, p.line) end
         _              => @match (t0, tf) begin
             (:( $v1[$i] ), :( $v2[$j] )) && if (v1 == v2 == p.v) end => 
-                :( time!($ocp, Index($i), Index($j), $tt) )
+                :( time!($ocp; ind0=$i, indf=$j, name=$tt) )
             _                                                        =>
 	            return __throw("bad time declaration", p.lnum, p.line) end
     end
diff --git a/test/runtests.jl b/test/runtests.jl
index 97ee2850..0f0eaf2e 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -9,55 +9,8 @@ const has = CTBase.has
 const replace_call = CTBase.replace_call
 const constraint_type = CTBase.constraint_type
 
-function __constraint!(
-    ocp::OptimalControlModel{<: TimeDependence, V}, 
-    type::Symbol, 
-    rg::Index, 
-    lb::Union{ctVector,Nothing}, 
-    ub::Union{ctVector,Nothing}, 
-    label::Symbol=CTBase.__constraint_label()) where {V <: VariableDependence} 
-
-    constraint!(ocp, type, rg=rg.val, f=nothing, lb=lb, ub=ub, label=label)
-    nothing # to force to return nothing
-
-end
-
-function __constraint!(
-    ocp::OptimalControlModel{<: TimeDependence, V}, 
-    type::Symbol, 
-    rg::OrdinalRange{<:Integer}, 
-    lb::Union{ctVector,Nothing}, 
-    ub::Union{ctVector,Nothing}, 
-    label::Symbol=CTBase.__constraint_label()) where {V <: VariableDependence} 
-
-    constraint!(ocp, type, rg=rg, f=nothing, lb=lb, ub=ub, label=label)
-    nothing # to force to return nothing
-
-end
-
-function __constraint!(
-    ocp::OptimalControlModel, 
-    type::Symbol, 
-    lb::Union{ctVector,Nothing}, 
-    ub::Union{ctVector,Nothing}, 
-    label::Symbol=CTBase.__constraint_label())
-
-    constraint!(ocp, type, rg=nothing, f=nothing, lb=lb, ub=ub, label=label)
-    nothing # to force to return nothing
-
-end
-
-function __constraint!(
-    ocp::OptimalControlModel{T, V}, 
-    type::Symbol, 
-    f::Function, 
-    lb::Union{ctVector,Nothing}, 
-    ub::Union{ctVector,Nothing}, 
-    label::Symbol=CTBase.__constraint_label()) where {T, V}
-
-    constraint!(ocp, type, rg=nothing, f=f, lb=lb, ub=ub, label=label)
-    nothing # to force to return nothing
-end
+# 
+include("utils.jl")
 
 #
 @testset verbose = true showtiming = true "Base" begin
diff --git a/test/test_model.jl b/test/test_model.jl
index 8e2f9a17..56229668 100644
--- a/test/test_model.jl
+++ b/test/test_model.jl
@@ -56,11 +56,11 @@ end
 
     ocp = Model()
 
-    i == 2 && begin time!(ocp, 0, 1) end
+    i == 2 && begin __time!(ocp, 0, 1) end
     i == 3 && begin state!(ocp, 2) end
     i == 4 && begin control!(ocp, 1) end
-    i == 5 && begin time!(ocp, 0, 1); state!(ocp, 2) end
-    i == 6 && begin time!(ocp, 0, 1); control!(ocp, 1) end
+    i == 5 && begin __time!(ocp, 0, 1); state!(ocp, 2) end
+    i == 6 && begin __time!(ocp, 0, 1); control!(ocp, 1) end
     i == 7 && begin state!(ocp, 2); control!(ocp, 1) end
 
     # constraint! 1
@@ -147,57 +147,48 @@ end
     ocp = Model(variable=true)
     @test !CTBase.__is_time_set(ocp)
     variable!(ocp, 1)
-    time!(ocp, 0, Index(1))
+    __time!(ocp, 0, Index(1))
     @test CTBase.__is_time_set(ocp)
 
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, Index(1), 1)
+    __time!(ocp, Index(1), 1)
     @test CTBase.__is_time_set(ocp)
     
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     @test CTBase.__is_time_set(ocp)
 
     ocp = Model()
-    time!(ocp, [0, 1])
-    @test CTBase.__is_time_set(ocp)
-
-    ocp = Model()
-    @test_throws MethodError time!(ocp, 0, Index(1))
-    @test_throws MethodError time!(ocp, Index(1), 1)
+    @test_throws MethodError __time!(ocp, 0, Index(1))
+    @test_throws MethodError __time!(ocp, Index(1), 1)
 
     ocp = Model(variable=true)
-    @test_throws UnauthorizedCall time!(ocp, 0, Index(1))
-    @test_throws UnauthorizedCall time!(ocp, Index(1), 1)
+    @test_throws UnauthorizedCall __time!(ocp, 0, Index(1))
+    @test_throws UnauthorizedCall __time!(ocp, Index(1), 1)
 
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, 0, Index(1))
-    @test_throws UnauthorizedCall time!(ocp, 0, Index(1))
-    @test_throws UnauthorizedCall time!(ocp, Index(1), 1)
-    @test_throws UnauthorizedCall time!(ocp, [0, 1])
-    @test_throws UnauthorizedCall time!(ocp, 0, 1)
+    __time!(ocp, 0, Index(1))
+    @test_throws UnauthorizedCall __time!(ocp, 0, Index(1))
+    @test_throws UnauthorizedCall __time!(ocp, Index(1), 1)
+    @test_throws UnauthorizedCall __time!(ocp, 0, 1)
 
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, Index(1), 1)
-    @test_throws UnauthorizedCall time!(ocp, 0, Index(1))
-    @test_throws UnauthorizedCall time!(ocp, Index(1), 1)
-    @test_throws UnauthorizedCall time!(ocp, [0, 1])
-    @test_throws UnauthorizedCall time!(ocp, 0, 1)
+    __time!(ocp, Index(1), 1)
+    @test_throws UnauthorizedCall __time!(ocp, 0, Index(1))
+    @test_throws UnauthorizedCall __time!(ocp, Index(1), 1)
+    @test_throws UnauthorizedCall __time!(ocp, 0, 1)
 
     ocp = Model(variable=true)
-    time!(ocp, [0, 1])
-    @test_throws UnauthorizedCall time!(ocp, 0, Index(1))
-    @test_throws UnauthorizedCall time!(ocp, Index(1), 1)
-    @test_throws UnauthorizedCall time!(ocp, [0, 1])
+    @test_throws UnauthorizedCall __time!(ocp, 0, Index(1))
+    @test_throws UnauthorizedCall __time!(ocp, Index(1), 1)
 
     ocp = Model(variable=true)
-    time!(ocp, 0, 1)
-    @test_throws UnauthorizedCall time!(ocp, 0, Index(1))
-    @test_throws UnauthorizedCall time!(ocp, Index(1), 1)
-    @test_throws UnauthorizedCall time!(ocp, [0, 1])
+    __time!(ocp, 0, 1)
+    @test_throws UnauthorizedCall __time!(ocp, 0, Index(1))
+    @test_throws UnauthorizedCall __time!(ocp, Index(1), 1)
 end
 
 @testset "Index" begin
@@ -394,38 +385,19 @@ end
 @testset "time!" begin
     # initial and final times
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     @test ocp.initial_time == 0
     @test ocp.final_time == 1
     @test ocp.time_name == "t"
 
     ocp = Model()
-    time!(ocp, 0, 1, "s")
+    __time!(ocp, 0, 1, "s")
     @test ocp.initial_time == 0
     @test ocp.final_time == 1
     @test ocp.time_name == "s"
     
     ocp = Model()
-    time!(ocp, 0, 1, :s)
-    @test ocp.initial_time == 0
-    @test ocp.final_time == 1
-    @test ocp.time_name == "s"
-
-    # initial and final times (bis)
-    ocp = Model()
-    time!(ocp, [0, 1])
-    @test ocp.initial_time == 0
-    @test ocp.final_time == 1
-    @test ocp.time_name == "t"
-
-    ocp = Model()
-    time!(ocp, [0, 1], "s")
-    @test ocp.initial_time == 0
-    @test ocp.final_time == 1
-    @test ocp.time_name == "s"
-
-    ocp = Model()
-    time!(ocp, [0, 1], :s)
+    __time!(ocp, 0, 1, :s)
     @test ocp.initial_time == 0
     @test ocp.final_time == 1
     @test ocp.time_name == "s"
@@ -433,21 +405,21 @@ end
     # initial time
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, 0, Index(1))
+    __time!(ocp, 0, Index(1))
     @test ocp.initial_time == 0
     @test ocp.final_time == Index(1)
     @test ocp.time_name == "t"
     
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, 0, Index(1), "s")
+    __time!(ocp, 0, Index(1), "s")
     @test ocp.initial_time == 0
     @test ocp.final_time == Index(1)
     @test ocp.time_name == "s"
 
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, 0, Index(1), :s)
+    __time!(ocp, 0, Index(1), :s)
     @test ocp.initial_time == 0
     @test ocp.final_time == Index(1)
     @test ocp.time_name == "s"
@@ -455,21 +427,21 @@ end
     # final time
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, Index(1), 1)
+    __time!(ocp, Index(1), 1)
     @test ocp.initial_time == Index(1)
     @test ocp.final_time == 1
     @test ocp.time_name == "t"
 
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, Index(1), 1, "s")
+    __time!(ocp, Index(1), 1, "s")
     @test ocp.initial_time == Index(1)
     @test ocp.final_time == 1
     @test ocp.time_name == "s"
 
     ocp = Model(variable=true)
     variable!(ocp, 1)
-    time!(ocp, Index(1), 1, :s)
+    __time!(ocp, Index(1), 1, :s)
     @test ocp.initial_time == Index(1)
     @test ocp.final_time == 1
     @test ocp.time_name == "s"
@@ -477,7 +449,7 @@ end
 
 @testset "is_min vs is_max" begin
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 1)
     objective!(ocp, :mayer, (x0, xf) -> x0[1] + xf[2])
@@ -485,7 +457,7 @@ end
     @test !is_max(ocp)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 1)
     objective!(ocp, :mayer, (x0, xf) -> x0[1] + xf[2], :max)
@@ -493,7 +465,7 @@ end
     @test !is_min(ocp)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 1)
     objective!(ocp, :lagrange, (x, u) -> 0.5u^2)
@@ -501,7 +473,7 @@ end
     @test !is_max(ocp)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 1)
     objective!(ocp, :lagrange, (x, u) -> 0.5u^2, :max)
@@ -509,7 +481,7 @@ end
     @test !is_min(ocp)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 1)
     objective!(ocp, :bolza, (x0, xf) -> x0[1] + xf[2], (x, u) -> x[1]^2 + u^2) # the control is of dimension 1
@@ -517,7 +489,7 @@ end
     @test !is_max(ocp)
     
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 1)
     objective!(ocp, :bolza, (x0, xf) -> x0[1] + xf[2], (x, u) -> x[1]^2 + u^2, :max) # the control is of dimension 1
@@ -528,21 +500,21 @@ end
 
 @testset "constraint! 1" begin
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     @test_throws IncorrectArgument __constraint!(ocp, :initial, [0, 1], [0, 1], :c0)
     __constraint!(ocp, :initial, 0, 0, :c0)
     __constraint!(ocp, :final, 1, 1, :cf)
     @test constraint(ocp, :c0)(12, ∅) == 12
     @test constraint(ocp, :cf)(∅, 12) == 12
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     __constraint!(ocp, :initial, [0, 1], [0, 1], :c0)
     __constraint!(ocp, :final, [1, 2], [1, 2], :cf)
     @test constraint(ocp, :c0)([12, 13], ∅) == [12, 13]
     @test constraint(ocp, :cf)(∅, [12, 13]) == [12, 13]
 
     # constraint already exists
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :initial, 0, 0, :c)
     @test_throws UnauthorizedCall __constraint!(ocp, :final, 0, 0, :c)
 
@@ -550,7 +522,7 @@ end
 
 @testset "constraint! 2" begin
     
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     x  = 12
     x0 = 0
     xf = 1
@@ -564,14 +536,14 @@ end
     @test constraint(ocp, :c00)(x, ∅) == x
     @test constraint(ocp, :cff)(∅, x) == x
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     x  = [12, 13]
     x0 = [0, 1]
     xf = [1, 2]
     @test_throws IncorrectArgument __constraint!(ocp, :initial, Index(2), x0, x0, :c0)
     @test_throws IncorrectArgument __constraint!(ocp, :final, Index(2), xf, xf, :cf)
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     x  = [12, 13]
     x0 = [0, 1]
     xf = [1, 2]
@@ -581,7 +553,7 @@ end
     @test constraint(ocp, :cf)(∅, x) == x[1:2]
 
     # constraint already exists
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     __constraint!(ocp, :initial, Index(1), 0, 0, :c)
     @test_throws UnauthorizedCall __constraint!(ocp, :final, Index(1), 0, 0, :c)
 
@@ -589,7 +561,7 @@ end
 
 @testset "constraint! 3" begin
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :initial, 0, 1, :c0)
     __constraint!(ocp, :final, 1, 2, :cf)
     __constraint!(ocp, :control, 0, 1, :cu)
@@ -599,7 +571,7 @@ end
     @test constraint(ocp, :cu)(12) == 12
     @test constraint(ocp, :cs)(12) == 12
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     __constraint!(ocp, :initial, [0, 1], [1, 2], :c0)
     __constraint!(ocp, :final, [1, 2], [2, 3], :cf)
     __constraint!(ocp, :control, [0, 1], [1, 2], :cu)
@@ -610,7 +582,7 @@ end
     @test constraint(ocp, :cs)([12, 13]) == [12, 13]
 
     # constraint already exists
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :initial, 0, 1, :c)
     @test_throws UnauthorizedCall __constraint!(ocp, :final, 0, 1, :c)
 
@@ -618,7 +590,7 @@ end
 
 @testset "constraint! 4" begin
  
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :initial, Index(1), 0, 1, :c0)
     __constraint!(ocp, :final, Index(1), 1, 2, :cf)
     __constraint!(ocp, :control, Index(1), 0, 1, :cu)
@@ -628,13 +600,13 @@ end
     @test constraint(ocp, :cu)(12) == 12
     @test constraint(ocp, :cs)(12) == 12
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     @test_throws IncorrectArgument __constraint!(ocp, :initial, Index(2), [0, 1], [1, 2], :c0)
     @test_throws IncorrectArgument __constraint!(ocp, :final, Index(2), [1, 2], [2, 3], :cf)
     @test_throws IncorrectArgument __constraint!(ocp, :control, Index(2), [0, 1], [1, 2], :cu)
     @test_throws IncorrectArgument __constraint!(ocp, :state, Index(2), [0, 1], [1, 2], :cs)
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     __constraint!(ocp, :initial, 1:2, [0, 1], [1, 2], :c0)
     __constraint!(ocp, :final, 1:2, [1, 2], [2, 3], :cf)
     __constraint!(ocp, :control, 1:2, [0, 1], [1, 2], :cu)
@@ -645,7 +617,7 @@ end
     @test constraint(ocp, :cs)([12, 13]) == [12, 13]
 
     # constraint already exists
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     __constraint!(ocp, :initial, Index(1), 0, 1, :c)
     @test_throws UnauthorizedCall __constraint!(ocp, :final, Index(1), 0, 1, :c)
 
@@ -653,7 +625,7 @@ end
 
 @testset "constraint! 5" begin
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :boundary, (x0, xf) -> x0+xf, 0, 0, :cb)
     __constraint!(ocp, :control, u->u, 0, 0, :cu)
     __constraint!(ocp, :state, x->x, 0, 0, :cs)
@@ -663,7 +635,7 @@ end
     @test constraint(ocp, :cs)(12) == 12
     @test constraint(ocp, :cm)(12, 13) == 12+13
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     __constraint!(ocp, :boundary, (x0, xf) -> x0[1]+xf[1], 0, 0, :cb)
     __constraint!(ocp, :control, u->u[1], 0, 0, :cu)
     __constraint!(ocp, :state, x->x[1], 0, 0, :cs)
@@ -673,7 +645,7 @@ end
     @test constraint(ocp, :cs)([12, 13]) == 12
     @test constraint(ocp, :cm)([12, 13], [14, 15]) == 12+14
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 3); control!(ocp, 3)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 3); control!(ocp, 3)
     __constraint!(ocp, :boundary, (x0, xf) -> [x0[1]+xf[1], x0[2]+xf[2]], [0, 0], [0, 0], :cb)
     __constraint!(ocp, :control, u->u[1:2], [0, 0], [0, 0], :cu)
     __constraint!(ocp, :state, x->x[1:2], [0, 0], [0, 0], :cs)
@@ -684,7 +656,7 @@ end
     @test constraint(ocp, :cm)([12, 13, 14], [15, 16, 17]) == [12+15, 13+16]
     
     # constraint already exists
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     __constraint!(ocp, :control, u->u, 0, 1, :c)
     @test_throws UnauthorizedCall __constraint!(ocp, :control, u->u, 0, 1, :c)
 
@@ -692,7 +664,7 @@ end
 
 @testset "constraint! 6" begin
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :boundary, (x0, xf) -> x0+xf, 0, 1, :cb)
     __constraint!(ocp, :control, u->u, 0, 1, :cu)
     __constraint!(ocp, :state, x->x, 0, 1, :cs)
@@ -702,7 +674,7 @@ end
     @test constraint(ocp, :cs)(12) == 12
     @test constraint(ocp, :cm)(12, 13) == 12+13
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     __constraint!(ocp, :boundary, (x0, xf) -> x0[1]+xf[1], 0, 1, :cb)
     __constraint!(ocp, :control, u->u[1], 0, 1, :cu)
     __constraint!(ocp, :state, x->x[1], 0, 1, :cs)
@@ -712,7 +684,7 @@ end
     @test constraint(ocp, :cs)([12, 13]) == 12
     @test constraint(ocp, :cm)([12, 13], [14, 15]) == 12+14
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     __constraint!(ocp, :boundary, (x0, xf) -> [x0[1]+xf[1], x0[2]+xf[2]], [0, 0], [1, 1], :cb)
     __constraint!(ocp, :control, u->u[1:2], [0, 0], [1, 1], :cu)
     __constraint!(ocp, :state, x->x[1:2], [0, 0], [1, 1], :cs)
@@ -732,7 +704,7 @@ end
     x0 = 7
     xf = 8
     ocp = Model(variable=true)
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     variable!(ocp, 4)
     state!(ocp, 1)
     control!(ocp, 1)
@@ -757,7 +729,7 @@ end
     x0 = 7
     xf = 8
     ocp = Model(variable=true)
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     variable!(ocp, 4)
     state!(ocp, 1)
     control!(ocp, 1)
@@ -784,19 +756,19 @@ end
 
 @testset "constraint! 9" begin
     
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     dynamics!(ocp, (x, u) -> x+u)
     @test ocp.dynamics(1, 2) == 3
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     dynamics!(ocp, (x, u) -> x[1]+u[1])
     @test ocp.dynamics([1, 2], [3, 4]) == 4
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 2)
     dynamics!(ocp, (x, u) -> [x[1]+u[1], x[2]+u[2]])
     @test ocp.dynamics([1, 2], [3, 4]) == [4, 6]
 
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     dynamics!(ocp, (x, u) -> [x[1]+u, x[2]+u])
     @test ocp.dynamics([1, 2], 3) == [4, 5]
 
@@ -804,7 +776,7 @@ end
 
 @testset "constraint! 10" begin
 
-    ocp = Model(autonomous=false); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(autonomous=false); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :initial, 0, 1, :c0)
     __constraint!(ocp, :final, 1, 2, :cf)
     @test constraint(ocp, :c0)(12, ∅) == 12
@@ -816,31 +788,31 @@ end
 
     dummy(u) = u^2 + u
 
-    ocp = Model(variable=true); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1); variable!(ocp,3)
+    ocp = Model(variable=true); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1); variable!(ocp,3)
     __constraint!(ocp, :state, 0, 1, :c0)
     __constraint!(ocp, :control, dummy, 1, 1, :c1)
     __constraint!(ocp, :variable, 1:2:3, [-Inf,-Inf], [0,0], :c2)
 
-    ocp_bis = Model(variable=true); time!(ocp_bis, 0, 1); state!(ocp_bis, 1); control!(ocp_bis, 1); variable!(ocp_bis,3)
+    ocp_bis = Model(variable=true); __time!(ocp_bis, 0, 1); state!(ocp_bis, 1); control!(ocp_bis, 1); variable!(ocp_bis,3)
     constraint!(ocp_bis, :state, lb=0, ub=1, label=:c0)
     constraint!(ocp_bis, :control, f=dummy, ub=1, lb=1, label=:c1)
     constraint!(ocp_bis, :variable, rg=1:2:3, ub=[0,0], label=:c2)
 
     @test ocp.constraints == ocp_bis.constraints
 
-    ocp_ter = Model(variable=true); time!(ocp_ter, 0, 1); state!(ocp_ter, 3); control!(ocp_ter, 1); variable!(ocp_ter,1)
+    ocp_ter = Model(variable=true); __time!(ocp_ter, 0, 1); state!(ocp_ter, 3); control!(ocp_ter, 1); variable!(ocp_ter,1)
     __constraint!(ocp_ter, :variable, 1, 1, :c0)
     __constraint!(ocp_ter, :control, dummy, 1, Inf, :c1)
     __constraint!(ocp_ter, :state, 1:2:3, [0,0], [0,0], :c2)
 
-    ocp_quad = Model(variable=true); time!(ocp_quad, 0, 1); state!(ocp_quad, 3); control!(ocp_quad, 1); variable!(ocp_quad,1)
+    ocp_quad = Model(variable=true); __time!(ocp_quad, 0, 1); state!(ocp_quad, 3); control!(ocp_quad, 1); variable!(ocp_quad,1)
     constraint!(ocp_quad, :variable, lb=1, ub=1, label=:c0)
     constraint!(ocp_quad, :control, f=dummy, lb=1, label=:c1)
     constraint!(ocp_quad, :state, rg=1:2:3, lb=[0,0], ub=[0,0], label=:c2)
 
     @test ocp_ter.constraints == ocp_quad.constraints
 
-    ocp_error = ocp_error = Model(variable=true); time!(ocp_error, 0, 1); state!(ocp_error, 3); control!(ocp_error, 1); variable!(ocp_error,1)
+    ocp_error = ocp_error = Model(variable=true); __time!(ocp_error, 0, 1); state!(ocp_error, 3); control!(ocp_error, 1); variable!(ocp_error,1)
     @test_throws UnauthorizedCall constraint!(ocp_error, :variable)
     @test_throws UnauthorizedCall constraint!(ocp_error, :control, f=dummy, label=:c1)
     @test_throws UnauthorizedCall constraint!(ocp_error, :state, rg=1:2:3, label=:c2)
@@ -851,7 +823,7 @@ end
 
 @testset "remove_constraint! and constraints_labels" begin
     
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 1); control!(ocp, 1)
     __constraint!(ocp, :boundary, (x0, xf) -> x0+xf, 0, 1, :cb)
     __constraint!(ocp, :control, u->u, 0, 1, :cu)
     k = constraints_labels(ocp)
@@ -866,7 +838,7 @@ end
 
 @testset "nlp_constraints without variable" begin
     
-    ocp = Model(); time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
+    ocp = Model(); __time!(ocp, 0, 1); state!(ocp, 2); control!(ocp, 1)
     __constraint!(ocp, :initial, Index(2), 10, 10, :ci)
     __constraint!(ocp, :final, Index(1), 1, 1, :cf)
     __constraint!(ocp, :control, 0, 1, :cu)
@@ -922,7 +894,7 @@ end
 @testset "nlp_constraints with variable" begin
     
     ocp = Model(variable=true)
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     variable!(ocp, 4)
     state!(ocp, 2)
     control!(ocp, 1)
@@ -990,35 +962,35 @@ end
     @test_throws UnauthorizedCall objective!(ocp, :bolza, (t0, x0, tf, xf) -> 0.5x0^2, (x, u) -> 0.5u^2)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     objective!(ocp, :lagrange, (x, u) -> 0.5u^2)
     @test ocp.lagrange(1, 2) == 2
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 2)
     objective!(ocp, :lagrange, (x, u) -> 0.5u[1]^2)
     @test ocp.lagrange([1, 2], [3, 4]) == 4.5
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     objective!(ocp, :mayer, (x0, xf) -> 0.5x0^2)
     @test ocp.mayer(2, 3) == 2
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 2)
     objective!(ocp, :mayer, (x0, xf) -> 0.5x0[1]^2)
     @test ocp.mayer([2, 3], [5, 6]) == 2
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     objective!(ocp, :bolza, (x0, xf) -> 0.5x0^2, (x, u) -> 0.5u^2)
@@ -1026,7 +998,7 @@ end
     @test ocp.lagrange(1, 2) == 2
     
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 2)
     objective!(ocp, :bolza, (x0, xf) -> 0.5x0[1]^2, (x, u) -> 0.5u[1]^2)
@@ -1034,7 +1006,7 @@ end
     @test ocp.lagrange([1, 2], [3, 4]) == 4.5
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 2)
     objective!(ocp, :lagrange, (x, u) -> 0.5u[1]^2)
@@ -1042,7 +1014,7 @@ end
     @test isnothing(ocp.mayer)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 2)
     control!(ocp, 2)
     objective!(ocp, :mayer, (x0, xf) -> 0.5x0[1]^2)
@@ -1058,8 +1030,8 @@ end
     @test_throws UnauthorizedCall variable!(ocp, 1)
 
     ocp = Model()
-    time!(ocp, 0, 1)
-    @test_throws UnauthorizedCall time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
+    @test_throws UnauthorizedCall __time!(ocp, 0, 1)
 
     ocp = Model()
     state!(ocp, 1)
@@ -1070,28 +1042,28 @@ end
     @test_throws UnauthorizedCall control!(ocp, 1)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     dynamics!(ocp, (x, u) -> x + u)
     @test_throws UnauthorizedCall dynamics!(ocp, (x, u) -> x + u)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     objective!(ocp, :mayer, (x0, xf) -> x0 + xf)
     @test_throws UnauthorizedCall objective!(ocp, :mayer, (x0, xf) -> x0 + xf)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     objective!(ocp, :lagrange, (x, u) -> x + u)
     @test_throws UnauthorizedCall objective!(ocp, :lagrange, (x, u) -> x + u)
 
     ocp = Model()
-    time!(ocp, 0, 1)
+    __time!(ocp, 0, 1)
     state!(ocp, 1)
     control!(ocp, 1)
     objective!(ocp, :bolza, (x0, xf) -> x0 + xf, (x, u) -> x + u)
diff --git a/test/test_print.jl b/test/test_print.jl
index 9d51cba1..e780703a 100644
--- a/test/test_print.jl
+++ b/test/test_print.jl
@@ -7,7 +7,7 @@ function test_print()
     ocp = Model(autonomous=false)
     state!(ocp, 2, "state", ["r", "v"]) # dimension of the state with the names of the components
     control!(ocp, 1)           # dimension of the control
-    time!(ocp, 0, 1, "s")    # initial and final time, with the name of the variable time
+    __time!(ocp, 0, 1, "s")    # initial and final time, with the name of the variable time
     __constraint!(ocp, :initial, [-1, 0], [-1, 0])
     __constraint!(ocp, :final  , [ 0, 0], [0, 0])
     A = [ 0 1
@@ -27,7 +27,7 @@ function test_print()
     ocp = Model(autonomous=false)
     state!(ocp, 1, "y") # dimension of the state with the names of the components
     control!(ocp, 1, "v")           # dimension of the control
-    time!(ocp, 0, 1, "s")    # initial and final time, with the name of the variable time
+    __time!(ocp, 0, 1, "s")    # initial and final time, with the name of the variable time
     __constraint!(ocp, :initial, -1, -1)
     __constraint!(ocp, :final  , 0, 0)
     dynamics!(ocp, (t, x, u) -> x+u)
@@ -44,7 +44,7 @@ function test_print()
     variable!(ocp, 1)
     state!(ocp, 1, "y") # dimension of the state with the names of the components
     control!(ocp, 2)           # dimension of the control
-    time!(ocp, 0, Index(1), "s")    # initial and final time, with the name of the variable time
+    __time!(ocp, 0, Index(1), "s")    # initial and final time, with the name of the variable time
     __constraint!(ocp, :initial, -1, -1)
     __constraint!(ocp, :final  , 0, 0)
     dynamics!(ocp, (t, x, u) -> x+u)
diff --git a/test/utils.jl b/test/utils.jl
new file mode 100644
index 00000000..d0a2b080
--- /dev/null
+++ b/test/utils.jl
@@ -0,0 +1,85 @@
+# time!
+
+function __time!(ocp::OptimalControlModel{<: TimeDependence, NonFixed}, t0::Time, indf::Index, name::String=CTBase.__time_name())
+    time!(ocp; t0=t0, indf=indf.val, name=name)
+end
+
+function __time!(ocp::OptimalControlModel, t0::Time, indf::Index, name::Symbol)
+    time!(ocp; t0=t0, indf=indf.val, name=name)
+end
+
+function __time!(ocp::OptimalControlModel{<: TimeDependence, NonFixed}, ind0::Index, tf::Time, name::String=CTBase.__time_name())
+    time!(ocp; ind0=ind0.val, tf=tf, name=name)
+end
+
+function __time!(ocp::OptimalControlModel, ind0::Index, tf::Time, name::Symbol)
+    time!(ocp; ind0=ind0.val, tf=tf, name=name)
+end
+
+function __time!(ocp::OptimalControlModel{<: TimeDependence, NonFixed}, ind0::Index, indf::Index, name::String=CTBase.__time_name())
+    time!(ocp; ind0=ind0.val, indf=indf.val, name=name)
+end
+
+function __time!(ocp::OptimalControlModel, ind0::Index, indf::Index, name::Symbol)
+    time!(ocp; ind0=ind0.val, indf=indf.val, name=name)
+end
+
+function __time!(ocp::OptimalControlModel, t0::Time, tf::Time, name::String=CTBase.__time_name())
+    time!(ocp; t0=t0, tf=tf, name=name)
+end
+
+function __time!(ocp::OptimalControlModel, t0::Time, tf::Time, name::Symbol)
+    time!(ocp; t0=t0, tf=tf, name=name)
+end
+
+# constraint!
+
+function __constraint!(
+    ocp::OptimalControlModel{<: TimeDependence, V}, 
+    type::Symbol, 
+    rg::Index, 
+    lb::Union{ctVector,Nothing}, 
+    ub::Union{ctVector,Nothing}, 
+    label::Symbol=CTBase.__constraint_label()) where {V <: VariableDependence} 
+
+    constraint!(ocp, type, rg=rg.val, f=nothing, lb=lb, ub=ub, label=label)
+    nothing # to force to return nothing
+
+end
+
+function __constraint!(
+    ocp::OptimalControlModel{<: TimeDependence, V}, 
+    type::Symbol, 
+    rg::OrdinalRange{<:Integer}, 
+    lb::Union{ctVector,Nothing}, 
+    ub::Union{ctVector,Nothing}, 
+    label::Symbol=CTBase.__constraint_label()) where {V <: VariableDependence} 
+
+    constraint!(ocp, type, rg=rg, f=nothing, lb=lb, ub=ub, label=label)
+    nothing # to force to return nothing
+
+end
+
+function __constraint!(
+    ocp::OptimalControlModel, 
+    type::Symbol, 
+    lb::Union{ctVector,Nothing}, 
+    ub::Union{ctVector,Nothing}, 
+    label::Symbol=CTBase.__constraint_label())
+
+    constraint!(ocp, type, rg=nothing, f=nothing, lb=lb, ub=ub, label=label)
+    nothing # to force to return nothing
+
+end
+
+function __constraint!(
+    ocp::OptimalControlModel{T, V}, 
+    type::Symbol, 
+    f::Function, 
+    lb::Union{ctVector,Nothing}, 
+    ub::Union{ctVector,Nothing}, 
+    label::Symbol=CTBase.__constraint_label()) where {T, V}
+
+    constraint!(ocp, type, rg=nothing, f=f, lb=lb, ub=ub, label=label)
+    nothing # to force to return nothing
+end
\ No newline at end of file