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

theorem :: REAL_2'66_2
  b <> 0 implies c - a / b = (c * b - a) / b
proof
  assume
A1: b<>0;
  thus c-a/b = -(a/b-c) .=-(a-c*b)/b by A1,Th126
    .=(-(a-c*b))/b by Lm17
    .=(c*b-a)/b;
end;
