
theorem
  for x be Element of NAT,
  y be Tuple of LenBSeq x, BOOLEAN
  st Nat2BL.x = y
  holds Absval(y) = x
  proof
    let x be Element of NAT,
    y be Tuple of LenBSeq x, BOOLEAN;
    assume AS: Nat2BL.x = y;
    Nat2BL.x = (LenBSeq x) -BinarySequence x by Def2;
    hence thesis by AS,LM007;
  end;
