theorem Th39:
  Sum -F = -(Sum F)
proof
  reconsider F1=F as FinSequence of COMPLEX by Lm2;
  thus Sum -F = compcomplex.(addcomplex $$ F1) by SEQ_4:51,52,SETWOP_2:31
    .= -(Sum F1) by BINOP_2:def 1
    .= -(Sum F);
end;
