let F be complex-valued FinSequence; :: thesis: Sum (- F) = - (Sum F)
reconsider F1 = F as FinSequence of COMPLEX by Lm4;
thus Sum (- F) = compcomplex . (addcomplex $$ F1) by SEQ_4:68, SEQ_4:69, SETWOP_2:42
.= - (Sum F1) by BINOP_2:def 1
.= - (Sum F) ; :: thesis: verum