subsetp list-1 list-2 &key key test test-not → generalized-boolean

list-1 — a proper list.

list-2 — a proper list.

test — a designator for a function of two arguments that returns a generalized boolean.

test-not — a designator for a function of two arguments that returns a generalized boolean.

key — a designator for a function of one argument, or nil.

generalized-boolean — a generalized boolean.

subsetp returns true if every element of list-1 matches some element of list-2, and false otherwise.

Whether a list element is the same as another list element is determined by the functions specified by the keyword arguments. The first argument to the :test or :test-not function is typically part of an element of list-1 extracted by the :key function; the second argument is typically part of an element of list-2 extracted by the :key function.

The argument to the :key function is an element of either list-1 or list-2; the return value is part of the element of the supplied list element. If :key is not supplied or nil, the list-1 or list-2 element itself is supplied to the :test or :test-not function.

(setq cosmos '(1 "a" (1 2))) → (1 "a" (1 2)) 
(subsetp '(1) cosmos) → true 
(subsetp '((1 2)) cosmos) → false 
(subsetp '((1 2)) cosmos :test 'equal) → true 
(subsetp '(1 "A") cosmos :test #'equalp) → true 
(subsetp '((1) (2)) '((1) (2))) → false 
(subsetp '((1) (2)) '((1) (2)) :key #'car) → true

Should be prepared to signal an error of type type-error if list-1 and list-2 are not proper lists.

Section 3.6 (Traversal Rules and Side Effects)

The :test-not parameter is deprecated.