+Also, the object created by @code{clifford_unit(mu, minkmetric())} is
+not aware about the symmetry of its metric, see the start of the pevious
+paragraph. A more accurate analog of 'dirac_gamma(mu)' should be
+specifies as follows:
+
+@example
+ clifford_unit(mu, indexed(minkmetric(),sy_symm(),varidx(symbol("i"),4),varidx(symbol("j"),4)));
+@end example
+