Lepton Rules

Leptons are fundamental particles.They can change into other leptons through weak interactions.They can also be produced or annihilated.

Lepton number is conserved in any change.Lepton Number is +1 for any lepton and -1 for any anti-leptonLeptons and hadrons interact. For example a neutrino or anti-neutrino can change into or form a corresponding charged lepton.

ν_e  + n   → p   +   e^-

but not:

ν_e +   n   → anti-p   +   e⁺

as lepton number would not be conserved.A Muon can decay into a muon neutrino

μ^-  → e^- + anti-ν_e   + ν_μ    

Charge is conserved and lepton number is conserved. But not:

μ^-  → e^- + anti-ν_e +   anti-ν_μ    

Charge is conserved but lepton number is not conserved.
An example is the muon which decays into an electron, a muon neutrino and an electron antineutrino.The muon can only change into a muon neutrino (not an antineutrino). The electron can only be created with an electron antineutrino.

μ^-  → e^- + anti-ν_e +   ν_μ    

So the lepton conservation rule is applied separately to electrons and muons.