theorem Th21:
  -(i|->r) = i|->-r
proof
  reconsider s=r as Element of REAL by XREAL_0:def 1;
  -(i|->s) = i|->(compreal.s) by FINSEQOP:16
    .= i|->-r by BINOP_2:def 7;
  hence thesis;
end;
