Xing, ZZ (reprint author), Inst High Energy Phys, POB 918 4, Beijing 100039, Peoples R China.
I follow a lesson learnt from Heisenberg's matrix Quantum Mechanics to study the property of lepton flavor mixing and CP violation. I show that the commutator of lepton mass matrices defined in vacuum keeps invariant under terrestrial matter effects within the four-neutrino mixing scheme. A set of model-independent sum rules for neutrino masses are obtained, and they can be generalized to hold for an arbitrary number of neutrino families. Useful sum rules for the rephasing-invariant measures of leptonic CP violation have also been found. Finally I present a generic formula of T-violating asymmetries applicable to the future long-baseline neutrino oscillation experiments.