2. Let be the class of computably enumerable (ce.) sets. Prove the following: (a) & is closed under union and intersection (b) & contains all the finite sets and cofinite sets of natural numbers. (c) If B E and g is a total computable function theng(B) E . and g(B) E 2. Let be the class of computably enumerable (ce.) sets. Prove the following: (a) & is closed under union and intersection (b) & contains all the finite sets and cofinite sets of natural numbers. (c) If B E and g is a total computable function theng(B) E . and g(B) E