 Similarly Woods' grammar for lunar was based on a certain kind of procedurally interpreted transition graph (an augmented transition network, or ATN), where the sentence subgraph might contain an edge labeled NP (analyze an NP using the NP subgraph) followed by an edge labeled VP (analogously interpreted). In both cases, local feature values (e.g., the number and person of a NP and VP) are registered, and checked for agreement as a condition for success. A closely related formalism is that of definite clause grammars (e.g., Pereira &amp; Warren 1982), which employ Prolog to assert “facts” such as that if the input word sequence contains an NP reaching from index I1 to index I2 and a VP reaching from index I2 to index I3, then the input contains a sentence reaching from index I1 to index I3. (Again, feature agreement constraints can be incorporated into such assertions as well.) Given the goal of proving the presence of a sentence, the goal-chaining mechanism of Prolog then provides a procedural interpretation of these assertions.