2. (5 pts) Suppose you are given the following axioms: ii. 9 s 12. iii vx x s x. iv x x sx0. Give a backward-chaining proof of the sentence 9+ -2 s 12. (Be sure, of course, to use only the axioms given here, not anything else you may know about arithmetic.) Show only the steps that leads to success, not the irrelevant steps