1. Define a predicate fifth/2 that, given a list as first argument, returns the fifth element of the list as its second argument. E.g.
| ?- fifth([1,2,3,4,5,6,7], X).
X = 5
yes
2.
Recall that every list (the empty list) has both a head and a tail. Use this
fact, and the head|tail notation to define a predicate
is_list/1 that returns true if its argument is a list (including the
empty list) and false otherwise.
3. Define a predicate cons/3, which takes a list as its
second argument, anything as its first argument and returns as its third
argument a new list in with the first argument as head and the second argument
as tail.