reserve X for set;
reserve a,b,c,k,m,n for Nat;
reserve i,j for Integer;
reserve r,s for Real;
reserve p,p1,p2,p3 for Prime;

theorem Th7:
  p1 divides p2 implies p1 = p2
  proof
    assume p1 divides p2;
    then p1 = 1 or p1 = p2 by INT_2:def 4;
    hence thesis by INT_2:def 4;
  end;
