diff --git a/src/Preferred_pref.cpp b/src/Preferred_pref.cpp
index 34b0dc5..b37fdcc 100644
--- a/src/Preferred_pref.cpp
+++ b/src/Preferred_pref.cpp
@@ -33,10 +33,22 @@ void Preferred::pref( AF* theAF, SetArguments* theC )
 
 	SetArguments e = SetArguments(),
 				 I = SetArguments();
-	Grounded( &e, &I );
+	// Avoid calling Grounded if useless
+	if ( theC->cardinality() <= 1 && *theC == *(theAF->get_arguments()) )
+	{
+		if ( debug )
+			cerr << "\tNo need to call Grounded.\n";
+
+		// Empty: no extensions => null iteration
+		// Singlet: still have to iterate over I
+		for ( SetArgumentsIterator it = theC->begin(); it != theC->end(); ++it )
+			e.add_Argument( *it );
+	}
+	else
+		Grounded( &e, &I );
 
 	if ( stages )
-		cerr << "e: " << e << endl << "I: " << I << endl; 
+		cerr << "\te: " << e << endl << "\tI: " << I << endl; 
 
 	// Convert Grounded's output into a Labelling
 	Labelling first = Labelling();
@@ -88,7 +100,7 @@ void Preferred::pref( AF* theAF, SetArguments* theC )
 				aLabelling != this->labellings.end(); ++aLabelling )
 		{
 			SetArguments O = SetArguments();
-			I = SetArguments();	// I already exists..
+			I = SetArguments();							// I already exists..
 
 			boundcond( *aSCC, (*aLabelling).inargs(), &O, &I );
 
@@ -98,46 +110,93 @@ void Preferred::pref( AF* theAF, SetArguments* theC )
 			if ( O.empty() )
 			{
 				if ( debug )
-					cerr << "\tCalling prefSAT.\n";
-
-				AF restricted = AF();
-				this->af->restrictTo( *aSCC, &restricted );
-
-				// TODO: prefSAT problem: the nodes in I are different from
-				// the nodes in the restricted AF.
-				// Temporary solution: rebuild I.
-				for ( SetArgumentsIterator it = restricted.begin(); it != restricted.end(); ++it )
+					cerr << "\tGoing to call prefSAT.\n";
+
+				// Avoid calling prefSAT if the two parameters are the same
+				// and the size is 2 or less:
+				// 	0:	out = { {} }
+				//	1:	out = { {singlet} }
+				//	2:	out = { {singlet}, {singlet} }
+				if ( (*aSCC)->cardinality() <= 2 && **aSCC == I )
 				{
-					try
+					if ( debug )
+						cerr << "\t\tNo need to call prefSAT.\n";
+
+					// Empty: no extensions => null iteration
+					// Singlet: still have to iterate over I
+					// Two element: Mutually exclusive arguments
+					for ( SetArgumentsIterator it = (*aSCC)->begin();
+							it != (*aSCC)->end(); ++it )
 					{
-						Argument* victim = I.getArgumentByName( (*it)->getName() );
-
-						// No exception: the Argument is inside I
-						// Remove it and substitute it with the new one
-						I.remove( victim );
-						I.add_Argument( *it );
+						Labelling* temp = new Labelling();
+						temp->add_label( *it, Labelling::lab_in );
+						p.labellings.push_back( *temp );
 					}
-					catch ( const std::out_of_range& oor )
+				}
+				else
+				{
+					AF restricted = AF();
+					this->af->restrictTo( *aSCC, &restricted );
+
+					// TODO: prefSAT problem: the nodes in I are different from
+					// the nodes in the restricted AF.
+					// Temporary solution: rebuild I.
+					for ( SetArgumentsIterator it = restricted.begin(); it != restricted.end(); ++it )
 					{
-						// The Argument is outside of I. Nothing to do.
+						try
+						{
+							Argument* victim = I.getArgumentByName( (*it)->getName() );
+
+							// No exception: the Argument is inside I
+							// Remove it and substitute it with the new one
+							I.remove( victim );
+							I.add_Argument( *it );
+						}
+						catch ( const std::out_of_range& oor )
+						{
+							// The Argument is outside of I. Nothing to do.
+						}
 					}
-				}
 
-				// Should be done iff I != Ø (doesn't prefSAT return Ø otherwise..?)
-				p.prefSAT( &restricted, &I );
+					if ( debug )
+						cerr << "\t\tCalling prefSAT.\n";
+
+					p.prefSAT( &restricted, &I );
+				}
 			}
 			else
 			{
 				if ( debug )
-					cerr << "\tCalling pref.\n";
+					cerr << "\tGoing to call pref.\n";
 
 				SetArguments restriction = SetArguments();
 				(*aSCC)->setminus( &O, &restriction );
-				AF restricted = AF();
-				this->af->restrictTo( &restriction, &restricted );
-				// TODO? the same as above for prefSAT.
+				if ( restriction.cardinality() <= 1 && restriction == I )
+				{
+					if ( debug )
+						cerr << "\t\tNo need to call pref.\n";
+
+					// Empty: no extensions => null iteration
+					// Singlet: still have to iterate over I
+					for ( SetArgumentsIterator it = I.begin();
+							it != I.end(); ++it )
+					{
+						Labelling* temp = new Labelling();
+						temp->add_label( *it, Labelling::lab_in );
+						p.labellings.push_back( *temp );
+					}
+				}
+				else
+				{
+					if ( debug )
+						cerr << "\tCalling pref.\n";
 
-				p.pref( &restricted, &I );
+					AF restricted = AF();
+					this->af->restrictTo( &restriction, &restricted );
+					// TODO? the same as above for prefSAT.
+
+					p.pref( &restricted, &I );
+				}
 			}
 
 			// prefSAT doesn't put newline at the end of its output...