Projections of Galois Rings

Let R and Rφ be associative rings with isomorphic subring lattices and φ be a lattice isomorphism (a projection) of the ring R onto the ring Rφ. We call Rφ the projective image of a ring R and call the ring R itself the projective preimage of a ring Rφ. We study lattice isomorphisms of Galois rings. By a Galois ring we mean a ring GR(pn, m) isomorphic to the factor ring K[x]/(f(x)), where K = Z/pnZ, p is a prime, f(x) is a polynomial of degree m irreducible over K, and (f(x)) is a principal ideal generated by the polynomial f(x) in the ring K[x]. Properties of the lattice of subrings of a Galois ring depend on values of numbers n and m. A subring lattice L of GR(pn, m) has the simplest structure for m = 1 (L is a chain) and for n = 1 (L is distributive). It turned out that only in these cases there are examples of projections of Galois ring onto rings that are not Galois rings. We prove the following result (Thm. 4). Let R = GR(pn, qm), where n > 1 and m > 1. Then Rφ ≅ R.