reserve s for set,
  i,j for natural Number,
  k for Nat,
  x,x1,x2,x3 for Real,
  r,r1,r2,r3,r4 for Real,
  F,F1,F2,F3 for real-valued FinSequence,
  R,R1,R2 for Element of i-tuples_on REAL;

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;
