> (though in order to be general a small amount of additional work is needed)
Not also that there are two methods of cycle detection for a reference counted GC that are not just a backup tracing-GC
1. Trial deletion (known since at least the mid 80s)
2. Various tracing systems that exploit extra information known to reference-counted systems e.g. Levanoni/Petrank[1] which actually implemented a reference counted GC for Java.
It would leak memory - reference counting cannot collect cycles (you need tracing GC for that, defeating the purpose of refcounting).