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

theorem Th181: :: REAL_2'38
  b<>0 & a*b=-b implies a=-1
proof
  assume that
A1: b<>0 and
A2: a*b=-b;
  a*(b*b")=(-b)*b" by A2,Th4;
  then a*1=(-b)*b" by A1,XCMPLX_0:def 7;
  hence a=-b*b" .=-1 by A1,XCMPLX_0:def 7;
end;
