
theorem RNS3:
  for x be Real, x1 be Point of RNS_Real st x=x1 holds -x = -x1
proof
  let x be Real, x1 be Point of RNS_Real;
  assume AS: x=x1;
  reconsider mx = -x as Point of RNS_Real by XREAL_0:def 1;
  x1 + mx = x + -x by AS,BINOP_2:def 9; then
  x1 + mx = 0.RNS_Real;
  hence thesis by RLVECT_1:def 10;
end;
