Lepton-number test of a decay channel
= Lepton-number test of a decay channel
Sum the <lepton numbers> of every final particle and compare with the initial sum. For example, $e^-\nu_e e^-e^+$ has $L_e=2$, whereas $e^-\bar\nu_e e^-e^+$ has $L_e=0$. The two differ physically; changing a neutrino bar is not a harmless typographic simplification. Overall <lepton number> is conserved by the usual charged-current <Standard Model> amplitudes with Dirac or massless <neutrinos>.