This works???

include/libsemigroups/sims2.hpp

@@ -110,7 +110,7 @@ namespace libsemigroups {
         for (size_t j = i + 1; j <= num_edges; ++j) {
           _used_slots[j] = _used_slots[i];
         }
-        LIBSEMIGROUPS_ASSERT(_used_slots[num_edges] < _2_sided_include.size());
+        LIBSEMIGROUPS_ASSERT(_used_slots[num_edges] <= _2_sided_include.size());
         return _used_slots[num_edges];
       }
     };

src/sims2.cpp

@@ -95,20 +95,20 @@ namespace libsemigroups {
     size_type start = current.num_edges;
     // TODO avoid extra copies here
     // One relation in _2_sided_include for every non-tree edge
-    while (start < _felsch_graph.definitions().size()) {
-      for (size_t i = start; i < _felsch_graph.definitions().size(); ++i) {
-        auto const& e = _felsch_graph.definitions()[i];  // TODO reference
-        if (current.target_is_new_node && e.first == current.source
-            && e.second == current.generator) {
-          continue;
-        }
-        word_type u = _2_sided_words[e.first];
-        u.push_back(e.second);
-        _2_sided_include.add_rule(
-            u,
-            _2_sided_words[_felsch_graph.target_no_checks(e.first, e.second)],
-            current.num_edges);
+    for (size_t i = start; i < _felsch_graph.definitions().size(); ++i) {
+      auto const& e = _felsch_graph.definitions()[i];  // TODO reference
+      if (current.target_is_new_node && e.first == current.source
+          && e.second == current.generator) {
+        continue;
       }
+      word_type u = _2_sided_words[e.first];
+      u.push_back(e.second);
+      _2_sided_include.add_rule(
+          u,
+          _2_sided_words[_felsch_graph.target_no_checks(e.first, e.second)],
+          current.num_edges);
+    }
+    while (start < _felsch_graph.definitions().size()) {
       // TODO different things if current.target is a new node
 
       auto first = _2_sided_include.begin(current.num_edges);