reserve a for set,
  i for Nat;

theorem Th6:
  for f be FinSequence st f = (*-->0).i holds len f = i
proof
  let p be FinSequence;
  assume
A1: p = (*-->0).i;
  p = i |-> 0 by A1,FINSEQ_2:def 6;
  hence thesis by CARD_1:def 7;
end;
