def distance1(word):
    """All edits that are one edit away from `word`."""
    letters = "abcdefghijklmnopqrstuvwxyz"
    splits = [(word[:i], word[i:]) for i in range(len(word) + 1)]
    deletes = [L + R[1:] for L, R in splits if R]
    transposes = [L + R[1] + R[0] + R[2:] for L, R in splits if len(R) > 1]
    replaces = [L + c + R[1:] for L, R in splits if R for c in letters]
    inserts = [L + c + R for L, R in splits for c in letters]

    return set(deletes + transposes + replaces + inserts)