reactivated an epsilon-tensor simplification hack because of a user request

diff --git a/ginac/tensor.cpp b/ginac/tensor.cpp
index 587a8170c38422c44b5719d5ca6bde2a0c9571a9..fb2e596e60bfc38f0d1641d40b76faf71df10652 100644 (file)
--- a/ginac/tensor.cpp
+++ b/ginac/tensor.cpp
@@ -510,10 +510,14 @@ bool tensepsilon::contract_with(exvector::iterator self, exvector::iterator othe
 
        } else if (other->return_type() == return_types::commutative) {
 
 
        } 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
                exvector c;
 
                // Handle all indices of the epsilon tensor