Do whatever it takes to make ``elem in gset`` true for each elem in ``elems``.
    
    See :func:`include`.

def include_many(gset, elems, truth_value=True):
    """Do whatever it takes to make ``elem in gset`` true for each elem in ``elems``.
    
    See :func:`include`.
    """
    extend = getattr(gset, 'extend', None)
    if extend is not None:
        extend(elems)
    elif hasattr(gset, '__setitem__'):
        gset.update((elem, truth_value) for elem in elems)
    elif hasattr(gset, 'update'):
        gset.update(elems)
    else:
        raise Error("gset is not a supported container.")