Interconvertibility of a Class of Set Constraints and Context-free-language Reachability 1

We show the interconvertibility of context-free-language reachability problems and a class of set-constraint problems: given a context-free-language reachability problem, we show how to construct a set-constraint problem whose answer gives a solution to the reachability problem; given a set-constraint problem, we show how to construct a context-free-language reachability problem whose answer gives a solution to the set-constraint problem. The interconvertibility of these two formalisms ooers an conceptual advantage akin to the advantage gained from the interconvertibility of nite-state automata and regular expressions in formal language theory, namely, a problem can be formulated in whichever formalism is most natural. It also ooers some insight into the \O(n 3) bottleneck" for diierent types of program-analysis problems, and allows results previously obtained for context-free-language reachability problems to be applied to set-constraint problems and vice versa.