theorem
  for f being FinSequence of REAL st len f = 3 holds f is Element of REAL 3
proof
    let f be FinSequence of REAL;
    assume
A1: len f = 3;
    reconsider x1 = f.1, x2 = f.2, x3 = f.3 as Element of REAL
           by XREAL_0:def 1;
    <*x1,x2,x3*> is Element of 3-tuples_on REAL by FINSEQ_2:104;
    hence thesis by A1,FINSEQ_1:45;
end;
