} else if (other->return_type() == return_types::commutative) {
-#if 0
- // This handles eps.i.j.k * p.j * p.k = 0
- // Maybe something like this should go to simplify_indexed() because
- // such relations are true for any antisymmetric tensors...
+#if 1
+ // This handles eps.i.j.k * p.j * p.k = 0 and related cases.
+ // Actually, simplify_indexed() can handle most of them on its own
+ // but one specific case that is not covered there is
+ // eps~mu.nu~i~j * p.mu * p~nu
+ // because of the difference in variance in the dummy indices mu
+ // and nu. Eventually, simplify_indexed() should be extended to
+ // handle this case, and this hack removed.
exvector c;
// Handle all indices of the epsilon tensor