theorem
  for a being object holds canFS({a}) = <* a *>
proof
  let a be object;
A1: rng canFS({a}) = {a} by FUNCT_2:def 3;
  len canFS({a}) = card {a} by Th92
    .= 1 by CARD_1:30;
  hence thesis by A1,Th39;
end;
