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

theorem
  for f being non empty FinSequence holds f = <*f.1*>^Del(f,1)
proof
  let f be non empty FinSequence;
  thus f = <*f.1*>^(f/^1) by Th29a
    .= <*f.1*>^Del(f,1) by Th3;
end;
