subsetp

(subsetp list1 list2 &key test key)

Returns true if every element of list1 is a member of list2, treating both as sets; returns false as soon as one element of list1 has no match. The comparison is eql by default; the optional :test keyword takes a function designator to use a different comparison, and the optional :key keyword takes a selector function applied to both compared elements. An empty list1 is always a subset.