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 Th17:
  m <> 0 implies
  denominator -(i/m) = m div ( (-i) gcd m ) &
  numerator -(i/m) = (-i) div ( (-i) gcd m )
  proof
    -(i/m) = (-i)/m;
    hence thesis by Th15;
  end;
