Index: ginac/indexed.cpp
===================================================================
RCS file: /home/cvs/GiNaC/ginac/indexed.cpp,v
retrieving revision 1.104
diff -u -r1.104 indexed.cpp
--- ginac/indexed.cpp	28 Jul 2006 22:34:28 -0000	1.104
+++ ginac/indexed.cpp	29 Aug 2006 17:24:02 -0000
@@ -628,6 +628,36 @@
 	}
 }
 
+/** Exchange variance of dummy indicies, helper class used
+ *   by reposition_dummy_indices */
+class exchange_varidx_variance_fct
+{
+	private:
+		varidx vi;
+	public:
+		explicit exchange_varidx_variance_fct(const varidx& vi_) : vi(vi_) { }
+		inline void operator()(ex& arg) const
+		{
+			if (arg.is_equal(vi) || arg.is_equal(vi.toggle_variance()))
+				arg = ex_to<varidx>(arg).toggle_variance();
+		}
+};
+
+/** Turn contraviariant varidx into covariant one, helper class used
+ *   by reposition_dummy_indices */
+class lower_dummy_varidx_fct
+{
+	private:
+		varidx vi;
+	public:
+		explicit lower_dummy_varidx_fct(const varidx& vi_): vi(vi_) { }
+		inline void operator()(ex & arg) const
+		{
+			if (arg.is_equal(vi))
+				arg = vi.toggle_variance();
+		}
+};
+
 /** Raise/lower dummy indices in a single indexed objects to canonicalize their
  *  variance.
  *
@@ -638,26 +668,41 @@
 bool reposition_dummy_indices(ex & e, exvector & variant_dummy_indices, exvector & moved_indices)
 {
 	bool something_changed = false;
-
+	exvector seq = ex_to<indexed>(e).seq;
+	
 	// If a dummy index is encountered for the first time in the
 	// product, pull it up, otherwise, pull it down
-	exvector::const_iterator it2, it2start, it2end;
-	for (it2start = ex_to<indexed>(e).seq.begin(), it2end = ex_to<indexed>(e).seq.end(), it2 = it2start + 1; it2 != it2end; ++it2) {
+	exvector::iterator it2, it2start, it2end;
+	for (it2start = seq.begin(), it2end = seq.end(), it2 = it2start + 1; it2 != it2end; ++it2)
+	{
 		if (!is_exactly_a<varidx>(*it2))
 			continue;
 
 		exvector::iterator vit, vitend;
-		for (vit = variant_dummy_indices.begin(), vitend = variant_dummy_indices.end(); vit != vitend; ++vit) {
-			if (it2->op(0).is_equal(vit->op(0))) {
-				if (ex_to<varidx>(*it2).is_covariant()) {
-					e = e.subs(lst(
-						*it2 == ex_to<varidx>(*it2).toggle_variance(),
-						ex_to<varidx>(*it2).toggle_variance() == *it2
-					), subs_options::no_pattern);
+		for (vit = variant_dummy_indices.begin(), vitend = variant_dummy_indices.end(); vit != vitend; ++vit)
+		{
+			if (it2->op(0).is_equal(vit->op(0))) 
+			{
+				if (ex_to<varidx>(*it2).is_covariant()) 
+				{
+					/*
+					 * N.B. we can't  use
+					 *
+					 *  e = e.subs(lst(
+					 *  *it2 == ex_to<varidx>(*it2).toggle_variance(),
+					 *  ex_to<varidx>(*it2).toggle_variance() == *it2
+					 *  ), subs_options::no_pattern);
+					 *
+					 * since this can trigger non-trivial repositioning of indices,
+					 * e.g. due to non-trivial symmetry properties of e, thus 
+					 * invalidating iterators
+					 */
+					std::for_each(seq.begin(), seq.end(), 
+							exchange_varidx_variance_fct(ex_to<varidx>(*it2)));
 					something_changed = true;
-					it2 = ex_to<indexed>(e).seq.begin() + (it2 - it2start);
-					it2start = ex_to<indexed>(e).seq.begin();
-					it2end = ex_to<indexed>(e).seq.end();
+					it2 = seq.begin() + (it2 - it2start);
+					it2start = seq.begin();
+					it2end = seq.end();
 				}
 				moved_indices.push_back(*vit);
 				variant_dummy_indices.erase(vit);
@@ -668,11 +713,12 @@
 		for (vit = moved_indices.begin(), vitend = moved_indices.end(); vit != vitend; ++vit) {
 			if (it2->op(0).is_equal(vit->op(0))) {
 				if (ex_to<varidx>(*it2).is_contravariant()) {
-					e = e.subs(*it2 == ex_to<varidx>(*it2).toggle_variance(), subs_options::no_pattern);
+					std::for_each(seq.begin(), seq.end(), 
+							lower_dummy_varidx_fct(ex_to<varidx>(*it2)));
 					something_changed = true;
-					it2 = ex_to<indexed>(e).seq.begin() + (it2 - it2start);
-					it2start = ex_to<indexed>(e).seq.begin();
-					it2end = ex_to<indexed>(e).seq.end();
+					it2 = seq.begin() + (it2 - it2start);
+					it2start = seq.begin();
+					it2end = seq.end();
 				}
 				goto next_index;
 			}
@@ -681,6 +727,13 @@
 next_index: ;
 	}
 
+	if (something_changed)
+	{
+		indexed ei_ = ex_to<indexed>(e);
+		ei_.seq = seq;
+		e = ei_;
+	}
+
 	return something_changed;
 }
 
Index: check/exam_paranoia.cpp
===================================================================
RCS file: /home/cvs/GiNaC/check/exam_paranoia.cpp,v
retrieving revision 1.20
diff -u -r1.20 exam_paranoia.cpp
--- check/exam_paranoia.cpp	1 May 2005 18:23:26 -0000	1.20
+++ check/exam_paranoia.cpp	29 Aug 2006 17:24:02 -0000
@@ -437,6 +437,33 @@
 	return result;
 }
 
+// Bug in reposition_dummy_indices() could result in correct expression
+// turned into one with inconsistent indices. Fixed on Aug 29, 2006
+static unsigned exam_paranoia17()
+{
+	varidx mu1(symbol("mu1"), 4);
+	varidx mu2(symbol("mu2"), 4);
+	varidx mu3(symbol("mu3"), 4);
+	varidx mu4(symbol("mu4"), 4);
+	varidx mu5(symbol("mu5"), 4);
+	varidx mu6(symbol("mu6"), 4);
+
+	exvector ev2;
+	ev2.push_back(mu3.toggle_variance());
+	ev2.push_back(mu6);
+	ev2.push_back(mu5.toggle_variance());
+	ev2.push_back(mu6.toggle_variance());
+	ev2.push_back(mu5);
+	ev2.push_back(mu3); 
+	// notice: all indices are contracted ...
+
+	ex test_cycl = indexed(symbol("A"), sy_cycl(), ev2);
+	test_cycl = test_cycl.simplify_indexed();
+	// ... so there should be zero free indices in the end.
+	return test_cycl.get_free_indices().size();
+}
+
+
 unsigned exam_paranoia()
 {
 	unsigned result = 0;
@@ -460,6 +487,7 @@
 	result += exam_paranoia14();  cout << '.' << flush;
 	result += exam_paranoia15();  cout << '.' << flush;
 	result += exam_paranoia16();  cout << '.' << flush;
+	result += exam_paranoia17();  cout << '.' << flush;
 	
 	if (!result) {
 		cout << " passed " << endl;