+ e = dirac_gamma(mu);
+ result += check_equal(dirac_trace(e), 0);
+
+ e = dirac_gamma(mu) * dirac_gamma(nu) * dirac_gamma(rho);
+ result += check_equal(dirac_trace(e), 0);
+
+ e = dirac_gamma5() * dirac_gamma(mu);
+ result += check_equal(dirac_trace(e), 0);
+
+ e = dirac_gamma5() * dirac_gamma(mu) * dirac_gamma(nu);
+ result += check_equal(dirac_trace(e), 0);
+
+ e = dirac_gamma5() * dirac_gamma(mu) * dirac_gamma(nu) * dirac_gamma(rho);
+ result += check_equal(dirac_trace(e), 0);
+
+ scalar_products sp;