  We analyze four-lepton contact interactions that lead to lepton flavor
violating processes, with violation of individual family lepton number but
total lepton number conserved. In an effective Lagrangian framework, the
assumption of gauge invariance leads to relations among branching ratios and
cross sections of lepton flavor violating processes. In this paper, we work out
how to use these relations systematically. We also study the consequences of
loop-induced processes.
