def search_sub(a, m):
    """
    Returns the index of the first inclusion of the sublist m in a. Returns
    None if m is not in a.
    """

    j = 0
    for i in range(len(a)):
        if a[i] != m[j]:
            j = 0
        else:
            j += 1
            if j == len(m):
                return i - len(m) + 1
    return None