A long time ago, I spent a few years working on garbage collection in the J9 Java VM. Yesterday, it was an insight from one of my favourite GC papers, A Unified Theory of Garbage Collection, which helped me solve a tricky problem. the problemUsing this machinery, I tried making an pmNodes attribute that produced a ProseMirror document for a given input. the solutionThen I remembered A Unified Theory of Garbage Collection, a 2004 OOPSLA paper by some former colleagues of mine:Tracing and reference counting are uniformly viewed as being fundamentally different approaches to garbage collection that possess very distinct performance properties. For every operation performed by the tracing collector, there is a precisely corresponding anti-operation performed by the reference counting collector.