reserve x,y,z for Real,
  a,b,c,d,e,f,g,h for Nat,
  k,l,m,n,m1,n1,m2,n2 for Integer,
  q for Rational;

theorem Th9:
  1,k are_coprime
proof
  1 gcd k = 1 by Th8;
  hence thesis by INT_2:def 3;
end;
