reserve i,j for Nat;

theorem Th14:
  for F1,F2 being FinSequence of REAL st len F1=len F2 holds F1 = F1 + F2 - F2
proof
  let F1,F2 be FinSequence of REAL;
  set n=len F1;
  assume len F1=len F2;
  then reconsider R1=F1, R2=F2 as Element of n-tuples_on REAL by FINSEQ_2:92;
  R1 = R1 + R2 - R2 by RVSUM_1:42;
  hence thesis;
end;
