reserve a, b, c, d, e for Complex;

theorem :: REAL_2'83:
  b <> 0 & d <> 0 & b <> -d & a / b = e / d implies a / b = (a + e) / (b + d )
proof
  assume that
A1: b<>0 and
A2: d<>0 and
A3: b<>-d and
A4: a/b=e/d;
  a*d=e*b by A1,A2,A4,Th95;
  then
A5: a*(b+d)=(a+e)*b;
  b+d<>0 by A3;
  hence thesis by A1,A5,Th94;
end;
