theorem Th88:
  Sum -F = -(Sum F)
proof
  reconsider F1=F as FinSequence of REAL by Lm2;
  thus Sum -F = compreal.(addreal $$ F1) by Th8,Th9,SETWOP_2:31
    .= -(Sum F1) by BINOP_2:def 7
    .= -(Sum F);
end;
