  We show that the L/E-flatness of the electron-like event ratio in the
Super-Kamiokande atmospheric neutrino data implies the equality of the
expectation values for the muon and tau neutrino masses. We establish this
result by obtaining a set of three constraints on the neutrino-oscillation
mixing matrix as contained in the indicated flatness. The resulting 3x3
neutrino-oscillation matrix depends only on one angle. A remarkable result that
follows directly from this matrix is the consistency between the mixing angles
observed by LSND and Super-Kamiokande.
