reserve p,q for Rational;
reserve g,m,m1,m2,n,n1,n2 for Nat;
reserve i,i1,i2,j,j1,j2 for Integer;

theorem Th19:
  m <> 0 implies
  denominator((m/i)") = m div ( m gcd i ) &
  numerator((m/i)") = i div ( m gcd i )
  proof
    (m/i)" = i/m by XCMPLX_1:213;
    hence thesis by Th15;
  end;
