def METHOD_NAME(entity, authz):
    """Implement the cross-effects of mutable flag and the authz
    system for serialisers and API."""
    if authz.is_admin:
        return True
    collection_id = ensure_dict(entity.get("collection")).get("id")
    collection_id = entity.get("collection_id", collection_id)
    if not entity.get("mutable"):
        return False
    return authz.can(collection_id, authz.WRITE)