A consequence of the Dirac equation is that the intrinsic parity of fermions and antifermions obey the relation P f ¯ ¯ P f = − − 1 , so particles and their antiparticles have the opposite parity. Single leptons can never be created or destroyed in experiments, as lepton number is a conserved quantity. This means experiments are unable to distinguish the sign of a leptons parity, so by convention it is chosen that leptons have intrinsic parity +1, antileptons have P = − − 1 . Similarly the parity of the quarks is chosen to be +1, and antiquarks is -1.