MEMBERP thing1 thing2
MEMBER? thing1 thing2

Outputs TRUE if thing1 is a member of thing2. Outputs FALSE, otherwise.

If thing2 is a list or an array, outputs TRUE if thing1 is EQUALP to an item of thing2, FALSE otherwise.

If thing2 is a word, outputs TRUE if thing1 is a single character that is EQUALP to a character in thing2, FALSE otherwise.

SHOW MEMBERP 1 [1 2 3]
true

SHOW MEMBERP 4 [1 2 3]
false

SHOW MEMBERP "b "abc
true

SHOW MEMBERP "bc "abc
false