lua garbage collection algorithms

http://stackoverflow.com/questions/1005169/lua-garbage-collection-of-tables-nested-tables

http://lua-users.org/wiki/GarbageCollectionTutorial

http://pgl.yoyo.org/luai/i/2.10+Garbage+Collection

http://pgl.yoyo.org/luai/i/2.8+Metatables

http://lua-users.org/wiki/EmergencyGarbageCollector