
theorem
  for a,b be Integer holds a div b = (-a) div (-b)
  proof
    let a,b be Integer;
    a div b = [\a/b/] by INT_1:def 9
    .= [\(-a)/(-b)/] by XCMPLX_1:191
    .= (-a) div (-b) by INT_1:def 9;
    hence thesis;
  end;
