Exercise 4.61: The following rules implement a
next-to relation that finds adjacent elements of a list:


(rule (?x next-to ?y in (?x ?y . ?u)))
(rule (?x next-to ?y in (?v . ?z))
      (?x next-to ?y in ?z))

What will the response be to the following queries?


(?x next-to ?y in (1 (2 3) 4))
(?x next-to 1 in (2 1 3 1))