One-bit counts between unique and sticky

Stoye's one-bit reference tagging scheme can be extended to local counts of two or more via two strategies. The first, suited to pure register transac tions, is a cache of referents to two shared references. The analog of Deut sch's and Bobrow's multiple-reference table, this cache is sufficient to ma nage small counts across successive assignment statements. Thus, accurate r eference counts above one can be tracked for short intervals, like those br idging one function's environment to its successor's. The second, motivated by runtime stacks that duplicate references, avoids c ounting any references from the stack. It requires a local pointer-inversio n protocol in the mutator, but one still local to the referent and the stac k frame. Thus, an accurate reference count of one can be maintained regardl ess of references from the recursion stack.