reserve X for set;
reserve a,b,c,k,m,n for Nat;
reserve i,j for Integer;
reserve r for Real;
reserve p,p1,p2 for Prime;

theorem Th63:
  a <> 1 & a <> n & a is non prime & a divides n implies
  not n is_a_product_of_two_different_primes by GR_CY_3:1;
