Two nodes are said to be C'01tgrutnJ if they represent equivalent expressions. Even if DO two nodes in the original type graph are congruent, after unification, it is possible for distinct nodes to be congruent. a) Give an algorithm to merge I class of mutually congruent nodes Rodes into a single node. ··b) Extend tbe algorithm in (a) to merge congruent nodes until no two distinct nodes are coagreent.