Xing, ZZ (reprint author), Inst High Energy Phys, POB 918, Beijing 100039, Peoples R China.
We show that the commutator of lepton mass matrices is invariant under terrestrial matter effects in the four-neutrino mixing scheme. A st of model-independent sum rules for neutrino masses, which may be generalized to hold for an arbitrary number of neutrino families, is for the first time uncovered. Useful sum rules for the rephasing-invariant measures of leptonic CP violation have also been found. Finally we present a generic formula of T-violating asymmetries and expect it to be applicable to the future long-baseline neutrino oscillation experiments.