An alternative: Two-mixing texture for three neutrinos or three-mixing texture for four neutrinos

The alternative formulated in the title has a chance to be settled, when th e existence of the LSND effect is experimentally excluded or confirmed. The first option, much discussed in literature, works in the case of three act ive neutrinos nu (e), nu (mu), nu (tau), when among their massive states nu (1), nu (2,) nu (3) there is no direct mixing between nu (1) and nu (3), a nd the mass hierarcy m(1)(2) less than or similar to m(2)(2) much less than m(3)(2) holds. This option is consistent with the observed deficits of sol ar nu (e)'s and atmospheric nu (mu)'s, if Deltam(21)(2) <-> Deltam(sol)(2) and Deltam(32)(2) <-> Deltam(atm)(2). On the other hand, the second option is an extension of the idea of the former to the case of four neutrinos nu (delta,) nu (e), nu (mu), nu (tau) (including one sterile neutrino nu (s)), when among their massive states nu (0), nu (1), nu (2), nu (3) there are n o direct mixings between nu (0) and nu (2,) nu (0) and nu (3), nu (1) and n u (3), and the mass hierarchy m(0)(2) less than or similar to m(1)(2) much less than m(2)(2) less than or similar to m(3)(2) is now valid. Such an opt ion, belonging to a class of textures widely discussed in literature, may b e consistent with the observed deficits of solar nu (e)'s and atmospheric n u (mu)'s as well as with the LSND appearance of nu (e)'s in the beam of acc elerator nu (mu)'s, if now Deltam(10)(2) <-> Deltam(sol)(2), Deltam(32)(2) <-> Deltam(atm)(2) and Deltam(21)(2) <-> Deltam(LSND)(2) (however, in the c ase of solar nu (e)'s the role of nu (s)'s in the disappearance of nu (e)'s is recently questioned). In both options, only the close neighbours in the hierarchies of massive neutrinos nu (1), nu (2), nu (3) and nu (0), nu (1) , nu (2), nu (3), respectively, mix directly. This characteristic feature o f the two-mixing texture for three neutrinos or the three-mixing texture fo r four neutrinos may be somehow physically significant.