Hello, I found that the code ex e=dirac_slash(a,4)*dirac_slash(b,4) +dirac_slash(b,4)*dirac_slash(a,4); cout << e << " has trace " << dirac_trace(e) << endl; e=canonicalize_clifford(e); cout << e << " has trace " << dirac_trace(e) << endl; gives the output b\*a\+a\*b\ has trace 4*b~symbol5*a.symbol5+4*a.symbol3*b~symbol3 2*b~symbol9*a.symbol9 has trace 2*b~symbol9*a.symbol9 I think this is wrong and that 2*b~symbol9*a.symbol9 should have been 2*ONE*b~symbol9*a.symbol9. A patch is attached. Bye, Chris