Hi Vladimir, I applied your and C.Dams' patch now. But I also applied a forgotten patch from you from December that changes ex clifford::get_metric(const ex & i, const ex & j) const from return indexed(metric, symmetric2(), i, j); to return indexed(metric, i, j); With this December patch the exams for clifford fail with ----------clifford objects: 2*ONE*[[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~nu~mu-2*[[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~mu~nu*ONE erroneously return ed 2*ONE*[[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~nu~mu-2*[[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~mu~nu*ONE instead of 0 [[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~mu~nu*e~lambda-[[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~nu~mu*e~lambda-0 erroneousl y returned [[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~mu~nu*e~lambda-[[-1,0,0,0],[0,0,0,0],[0,0,1,0],[0,0,0,-1]]~nu~mu*e~lambda i nstead of 0 Without it, it produces no error. The December patch makes sense to me, because the tutorial promises that one can use non-symmetric metrics. Am I wrong here? So, what should I do about it? Regards, Jens