theorem
  for F being FinSequence of COMPLEX holds Sum -F = -(Sum F)
proof
  let F be FinSequence of COMPLEX;
  thus Sum -F = addcomplex $$(compcomplex*F) by SEQ_4:def 8
    .= compcomplex.(addcomplex $$ F) by SEQ_4:51,52,SETWOP_2:31
    .= -(Sum F) by BINOP_2:def 1;
end;
