reserve s for set,
  i,j for Nat,
  c,c1,c2,c3 for Complex,
  F,F1,F2 for complex-valued FinSequence,
  R,R1,R2 for i-element complex-valued FinSequence;

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;
