Another fix for cyclicity

When an ordering is found to be the best, it wins over all previously tried candidates, not just the most recent one. This oversight becomes apparent when looking at the recent discussion on the Cadabra Q&A forum.

Author: cbehan

core/algorithms/sort_product.cc

@@ -142,8 +142,7 @@ Algorithm::result_t sort_product::apply(iterator& st)
 					compare.clear();
 					auto es=compare.equal_subtree(one, two);
 					if(es==Ex_comparator::match_t::no_match_greater || es==Ex_comparator::match_t::match_index_greater) {
-						--candidate;
-						candidate=candidates.erase(candidate);
+						candidate=candidates.erase(candidates.begin(), candidate);
 						one=candidate->at(digit-1);
 						++candidate;
 						}