reserve a,b,i,k,m,n for Nat;
reserve s,z for non zero Nat;
reserve r for Real;
reserve c for Complex;
reserve e1,e2,e3,e4,e5 for ExtReal;

theorem Th13:
  0 < m implies m gcd n <= m
  proof
    m gcd n divides m by INT_2:def 2;
    hence thesis by INT_2:27;
  end;
