iscleared
if (!hasclears && iscleared(g, gval(n))) /* is there a white value? */
else if (iscleared(g, gkey(n))) { /* key is not marked (yet)? */
if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
if (iscleared(g, o)) /* value was collected? */
if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {