reserve i,j,k,n for Nat;
reserve D for non empty set,
  p for Element of D,
  f,g for FinSequence of D;

theorem Th17:
  for f being FinSequence, i being Nat holds len(f|i) <= i
proof
  let f be FinSequence, i be Nat;
  i <= len f implies len(f|i) = i by FINSEQ_1:59;
  hence thesis by FINSEQ_1:58;
end;
