If you want to know that a list belongs to another list, you can use the isSubset() method:

const myList = List.of(
  List.of(1, 2, 3),
  List.of(4, 5, 6),
  List.of(7, 8, 9)
);
const isSubset = List.of(1, 4, 7)
  .isSubset(myList.flatten());

console.log('isSubset', isSubset);
// -> isSubset true

The myList collection is a list of lists. So once you flatten it, you can pass it to the isSubset() method when it's called on the list: List.of(1, 4, 7). This returns true because myList contains each of these values.