ContainsOnly

ContainsOnly[list1, list2] yields True if list1 contains only elements that appear in list2.

ContainsOnly[list2] is an operator form that yields True when the object to which it is applied contains only elements that appear in list2.

Examples

Check if a list contains only specified elements:

ContainsOnly[{a, b, a}, {a, b, c}]
(* True *)

ContainsOnly[{a, b, d}, {a, b, c}]
(* False *)

Please visit the official Wolfram Language Reference for more details.