14. Consider the following logic program:

ap(emp, L, L) .

ap(c(H, T), L, c(H, R)) ←

ap(T, L, R) .

adj(A, B, L) ←

ap(F, c(A, c(B, E)), L) .

(a) Give a top-down derivation (including all substitutions) for one answer to the query

???????????? adj

(b, Y, c

(a, c

(b, c

(b, c

(a, emp))))) .

(b) Are there any other answers? If so, explain where a different choice could be made in the derivation in the previous answer, and continue the derivation, showing another answer. If there are no other answers, explain why not.
[You are meant to do this exercise as if you were a computer, without knowing what the symbols mean. If you want to give a meaning to this program, you could read ap as append, c as cons, emp as empty, and adj as adjacent.]