def compare_strings(old_string, new_string):
    """Splits a string by spaces, and compares the lists. Then, returns a dictionary containing the following results:

    `equal` is a list of words in common.

    `removed` is a list of words that ARE in old_string, but ARE NOT in new_string.

    `added` is a list of words that ARE NOT in old_string, but ARE in new_string.
    """
    old_string = old_string.split(" ")
    new_string = new_string.split(" ")

    equal_words = list(set(old_string).intersection(new_string))
    removed_words = list(set(old_string) - set(new_string))
    added_words = list(set(new_string) - set(old_string))

    return {"equal": equal_words, "removed": removed_words, "added": added_words}