After reviewing some notions of the formal theory of diierential equations we discuss the completion of a given system to an involutive one. As applications to symmetry theory we study the eeects of local solvability and of gauge symmetries, respectively. We consider non-classical symmetry reductions and more general reductions using diierential constraints.

Theorem (1) There is an involution C of G satisfying: C(h) = h −1 (h ∈ H); (2) C(g) ∼ g −1 for all semisimple elements g; (3) Any two such involutions are conjugate by an inner automorphism;

It has been recently proved that a variety of associative PI-superalgebras with graded involution finite basic rank over field characteristic zero is minimal fixed ⁎-graded exponent if, and only it generated by subalgebra an upper block triangular matrix algebra, A:=UTZ2⁎(A1,…,Am), equipped suitable elementary Z2-grading involution. Here we give necessary sufficient conditions so IdZ2⁎(A) facto...