Consideration is given to the uniqueness of solutions of both classica
l and new problems of the theory of systems or, more precisely, to a s
trict definition of the equivalence class of solutions and to their su
fficient conditions. We assert that progress in this field would enabl
e one not only to shed new light on the traditional problems of the th
eory of systems, but what as more important, to tackle in formal mathe
matical terms the topical problem of functional integration of systems
.