Dear developers, Could you change the line if (get_all_dummy_indices(m).size() > 0) { that occurs in the function power::expand_mul in power.cpp into if (get_all_dummy_indices(m).size() > 0 && n.is_positive()) { Reason: I sometimes use algebraic substitution for expressions involving indices. For instance using the pattern indexed(UL1inv,wildgen,wildgen2)*indexed(UL1,wildgen2,wildgen3) ==delta_tensor(wildgen,wildgen3) to cancel a matrix multiplied with its inverse. Internally, algebraic subsitution divides by the factors it wants to get rid of but since Vladimir Kisils patch this goes wrong if these factors contain a contraction. Best wishes, Chris