4.

(a) Define the PROLOG predicate

max(X, Y, Max)

so that max is the greater of two numbers X and Y.

(b) Define the PROLOG predicate

sumlist(List, Sum)

so that sumlist is the sum of a given list of numbers List.

(c) Define the PROLOG predicate

count(a, L, C)

so that C is the number of occurrences of an element a in a list L at superficial level.

Example:

?- count(a,[a,b,c,[a,c],a],C).

C = 2