SML exercises

1. Write an SML function that tests whether or not two sets (stored as
lists) are equal. (Hint: you may want to write auxiliary functions to
help do this task).

2. Write an SML function that returns a new list built from the
elements of a list x that satisfy a predicate pred.

3. Write an SML function that tests whether or not all the elements of
a list satisfy some predicate (i.e., forall). Use this function to
build another function that tests if 2 sets (stored as lists) are
disjoint.