  -   $y \lor (y \to (x \lor  y)) \approx (0 \to x) \lor (x \to y)$\  -   $x \lor [y \to (y \to x)^*] \approx x \lor y \lor (y \to x)$\  -   $[\{x \lor (x \to y^*)\} \to (x \to y^*)] \lor x \lor y^* \approx 0$\  -   $x \lor (y \to z) \approx (x \lor  y) \to (x \lor z)$