
theorem Th11:
  for T be Tree st T = {0,1}* for n be non zero Nat
  for y be Element of n-tuples_on BOOLEAN holds y in T-level n
proof
  let T be Tree;
  assume
A1: T = {0,1}*;
  let n be non zero Nat;
  let y be Element of n-tuples_on BOOLEAN;
  y in { w where w is Element of T : len w = n } by A1;
  hence thesis by TREES_2:def 6;
end;
