theorem
  m <> 0 implies
  denominator -(i/m) = m / ( (-i) gcd m ) &
  numerator -(i/m) = (-i) / ( (-i) gcd m )
  proof
    assume
A1: m <> 0;
    hence denominator -(i/m) = m div ( (-i) gcd m ) by Th17
    .= m / ( (-i) gcd m ) by Th8;
    thus numerator -(i/m) = (-i) div ( (-i) gcd m ) by A1,Th17
    .= (-i) / ( (-i) gcd m ) by Th7;
  end;
