a. Compose the substitution sets {a/X, Y/Z} and {X/W, b/Y}. b. Prove that composition of substitution sets is associative. c. Construct an example to show that composition is not commutative....

a. Compose the substitution sets {a/X, Y/Z} and {X/W, b/Y}.

b. Prove that composition of substitution sets is associative.

c. Construct an example to show that composition is not commutative.

Implement the unify algorithm of Section 2.3.2 in the computer language of your choice.