If, as suggested by the Super-Kamiokande results, ${\nu }_{\mu }$ and ${\nu }_{\tau }$ are maximally and “rapidly” ( $\Delta m^2\approx 2.2\times {10}^{-3\mathrm{}}{\mathrm{eV}}^2$) mixed, this alone determines the mapping from current to mass eigenstates up to one rotation angle $\theta$ mixing ${\nu }_e$ “more slowly” with a particular, equal-weight combination of ${\nu }_{\mu }$ and ${\nu }_{\tau }$. For $\sin 2\theta =1\mathrm{}$, the resulting minimal number of free parameters, yet maximal mixing, shows agreement, with minor modifications, between extant observations of solar neutrinos and predictions by the standard solar model.

• Received 1 July 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.5730