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

theorem :: REAL_2'40
  b <> 0 & b / a = - b implies a = -1
proof
  assume that
A1: b<>0 and
A2: b/a=-b;
  a <> 0 by A1,A2,Th49;
  then b=(-b)*a by A2,Lm3;
  then b=-b*a;
  hence thesis by A1,A2,Th181;
end;
