def is_interior_link(link, grid):
    """Return True if both nodes are core; False otherwise."""
    return (
        grid.status_at_node[grid.node_at_link_tail[link]] == grid.BC_NODE_IS_CORE
        and grid.status_at_node[grid.node_at_link_head[link]] == grid.BC_NODE_IS_CORE
    )