def plaquette_to_sites(p):
    """Turn a plaquette ``((i0, j0), (di, dj))`` into the sites it contains.

    Examples
    --------

        >>> plaquette_to_sites([(3, 4), (2, 2)])
        ((3, 4), (3, 5), (4, 4), (4, 5))
    """
    (i0, j0), (di, dj) = p
    return tuple((i, j)
                 for i in range(i0, i0 + di)
                 for j in range(j0, j0 + dj))