theorem
  Sum -p = -(Sum p)
proof
  the addF of K is having_an_inverseOp & the_inverseOp_wrt the addF of K =
  ( comp K) by Th14,Th15;
  hence Sum -p = (comp K).(Sum p) by Th8,SETWOP_2:31
    .= -(Sum p) by VECTSP_1:def 13;
end;
