“…The reduction method [6] is free of a number of limitations of the comparison method and consists in determining non trivial solutions D of logical equations, such as equa tions of the form D & A → (P' → P), where, as previ ously, the known terms A, P', and P of the equation must satisfy certain consistency conditions. In [7], for polybasic algebraic systems and their properties expressible in a language with appropriate signature, a method for obtaining solutions D without the a priori conditions A was proposed. Other known methods for solving logical equations of general and special form are not applicable, because they do not take into account the specifics of the preservation problem under consideration.…”