def substrings(seq):
    """ Returns a set of all the substrings of s.
    Recall we can compute a substring using s[i:j] where 0 <= i, j < len(s).

    Example:
    >>> substrings("abc")
    "a", "ab", "abc", "b", "bc", "c"
    """
    subs = set()
    for i in range(len(seq)): #determine the starting index
        for j in range(i + 1, len(seq) + 1): #determine the ending index
            subs.add(seq[i:j])
    return subs