On a reduction of nonlinear evolution and wave type equations via non-point symmetry method

We study the symmetry reduction of nonlinear evolution and wave type differential equations by using operators of non--point symmetry. In our approach we use both operators of classical and conditional symmetry. It appears that the combination of non--point and conditional symmetry enables us to construct not only solutions but B\"acklund transformations too for the equation under study.We show that the method can be applied to nonevolutionary partial differential equations.