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
  n is_a_product_of_two_different_primes implies
  for a,b st a <> 1 & b <> 1 & n = a*b holds a is prime & b is prime by Th59;
