theorem Th56:
  Eval(-p) = -Eval(p)
  proof
    let r be Element of REAL;
    set s = In(r,F);
    (Eval(p)).r = eval(p,s) by POLYNOM5:def 13;
    hence (-Eval(p)).r = -eval(p,s) by VALUED_1:8
    .= eval(-p,s) by POLYNOM4:20
    .= (Eval(-p)).r by POLYNOM5:def 13;
  end;
