def inactive_regions(x, k, abs_tol=0):
    """ Seek periods of length k that of small deviation

    Examples
    --------

    >>> inactive_regions([1, 1, 2, 3, 3, 3, 3, 3, 4, 5, 5, 6], 2)
    [(1, slice(0, 2)), (3, slice(3, 8)), (5, slice(9, 11))]
    """
    start = 0
    result = []
    for i in range(len(x)):
        if abs(x[i] - x[start]) > abs_tol:  # End of chain
            if (i - start) >= k:
                result.append((x[start], slice(start, i)))
            start = i
    return result