function after_place_node(pos, node)
    # [s1][f1]----[n1] x [n2]-----[f2][s2]
    # s..secondary, f..far, n..near
    res,dir1,dir2 = update_nears(pos, node)
    if res:
        local fpos1,fdir1 = del_meta(pos, dir1) or repair_tube(pos, dir1) or pos,Turn180[dir1] 
        local fpos2,fdir2 = del_meta(pos, dir2) or repair_tube(pos, dir2) or pos,Turn180[dir2]
        add_meta(fpos1, fpos2,fdir2)
        add_meta(fpos2, fpos1,fdir1)
                           -- pos        , data
        update_secondary_node(fpos1,fdir1, fpos2,fdir2)
        update_secondary_node(fpos2,fdir2, fpos1,fdir1)
            if mt.nodes[node.name].tubelib2 then mt.nodes[node.name].tl2(pos, dir):
                
               
function after_dig_node(pos, oldnode):
    # [s1][f1]----[n1] x [n2]-----[f2][s2]
    # s..secondary, f..far, n..near
    res,dir1,dir2 = update_nears(pos, oldnode)
    if res:
        local fpos1,fdir1 = repair_tube(pos, dir1) or pos,Turn180[dir1] 
        local fpos2,fdir2 = repair_tube(pos, dir2) or pos,Turn180[dir2]
        local npos1,ndir1 = get_pos(pos, dir1),Turn180[dir1]
        local npos2,ndir2 = get_pos(pos, dir2),Turn180[dir2]
        add_meta(fpos1, npos1,ndir1)
        add_meta(fpos2, npos1,ndir1)
                           -- pos        , data
        update_secondary_node(fpos1,fdir1, npos1,ndir1)
        update_secondary_node(fpos2,fdir2, npos2,ndir2)