  A four-neutrino effective texture is described, where a sterile neutrino
mixes nearly maximally with the electron neutrino and so, is responsible for
the deficit of solar $\nu_e $'s (according to the large-angle MSW solution or
vacuum solution, of which the former is selected a posteriori). But, while
maximal mixing of muon neutrino with tauon neutrino causes the deficit of
atmospheric $\nu_\mu $'s, the original magnitude of LSND effect is reduced by
as much as four orders, becoming unobservable.
