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

theorem Th7: :: REAL_2'37
  b <> 0 & a * b = b implies a = 1
proof
  assume that
A1: b<>0 and
A2: a*b=b;
  a*b*b"=1 by A1,A2,XCMPLX_0:def 7;
  then a*1=1 by A2,Th4;
  hence thesis;
end;
