lua_insert
lua_insert(L, -2); /* put value below buffer */
lua_insert(L, -2); /* place '.' between the two names */
lua_insert(L, -(nup + 1)); /* move library table to below upvalues */
lua_insert(L, -2);
lua_insert(L, -(r + 1));
lua_insert(L, -2);
LUA_API void (lua_insert) (lua_State *L, int idx);