On the analogues and generalizations of squire's theorem

Assertions consistent with Squire's theorem /1/ based on the simultaneous or separate consideration of the factors responsible for the non-linearity of the motion and the non-stationarity of the fluid flow whose stability is investigated, are studied. The results may be of interest from the point of view of the practical applications, and can also be used to solve the problem of the degree of generality of the reasons governing the existence of assertions of the type of Squire's theorem.