Rewrite tensor network constructors

src/abstractitensornetwork.jl

@@ -116,7 +116,8 @@ end
 # TODO: broadcasting
 
 function Base.union(tn1::AbstractITensorNetwork, tn2::AbstractITensorNetwork; kwargs...)
-  tn = ITensorNetwork(union(data_graph(tn1), data_graph(tn2)); kwargs...)
+  # TODO: Use a different constructor call here?
+  tn = _ITensorNetwork(union(data_graph(tn1), data_graph(tn2)); kwargs...)
   # Add any new edges that are introduced during the union
   for v1 in vertices(tn1)
     for v2 in vertices(tn2)
@@ -129,7 +130,8 @@ function Base.union(tn1::AbstractITensorNetwork, tn2::AbstractITensorNetwork; kw
 end
 
 function NamedGraphs.rename_vertices(f::Function, tn::AbstractITensorNetwork)
-  return ITensorNetwork(rename_vertices(f, data_graph(tn)))
+  # TODO: Use a different constructor call here?
+  return _ITensorNetwork(rename_vertices(f, data_graph(tn)))
 end
 
 #
@@ -736,7 +738,8 @@ function norm_network(tn::AbstractITensorNetwork)
     setindex_preserve_graph!(tndag, dag(tndag[v]), v)
   end
   tnket = rename_vertices(v -> (v, 2), data_graph(prime(tndag; sites=[])))
-  tntn = ITensorNetwork(union(tnbra, tnket))
+  # TODO: Use a different constructor here?
+  tntn = _ITensorNetwork(union(tnbra, tnket))
   for v in vertices(tn)
     if !isempty(commoninds(tntn[(v, 1)], tntn[(v, 2)]))
       add_edge!(tntn, (v, 1) => (v, 2))
@@ -809,6 +812,9 @@ end
 
 Base.show(io::IO, graph::AbstractITensorNetwork) = show(io, MIME"text/plain"(), graph)
 
+# TODO: Move to an `ITensorNetworksVisualizationInterfaceExt`
+# package extension (and define a `VisualizationInterface` package
+# based on `ITensorVisualizationCore`.).
 function ITensorVisualizationCore.visualize(
   tn::AbstractITensorNetwork,
   args...;
@@ -865,6 +871,7 @@ function site_combiners(tn::AbstractITensorNetwork{V}) where {V}
   return Cs
 end
 
+# TODO: Combine with `insert_links`.
 function insert_missing_internal_inds(
   tn::AbstractITensorNetwork, edges; internal_inds_space=trivial_space(tn)
 )
@@ -880,12 +887,17 @@ function insert_missing_internal_inds(
   return tn
 end
 
+# TODO: Combine with `insert_links`.
 function insert_missing_internal_inds(
   tn::AbstractITensorNetwork; internal_inds_space=trivial_space(tn)
 )
   return insert_internal_inds(tn, edges(tn); internal_inds_space)
 end
 
+# TODO: What to output? Could be an `IndsNetwork`. Or maybe
+# that would be a different function `commonindsnetwork`.
+# Even in that case, this could output a `Dictionary`
+# from the edges to the common inds on that edge.
 function ITensors.commoninds(tn1::AbstractITensorNetwork, tn2::AbstractITensorNetwork)
   inds = Index[]
   for v1 in vertices(tn1)