:<math>\forall X, Y, Z(arc(X,Z)\land path(Z,Y) \rightarrow path(X,Y)).</math>
The logical reading frees the reader from needing to have any knowledge aboutknow how the knowledgeclause is used to solve problems. The knowledgeclause can be used top-down, as in Prolog, to reduce problems to subproblems. Or it can be used [[forward chaining|bottom-up (or forwards)]], as in [[Datalog]], to derive conclusions from conditions. This [[separation of concerns]] is a form of [[Abstraction (computer science)|abstraction]], which [[Algorithm#Algorithm = Logic + Control|separates declarative knowledge from problem solving methods]].<ref>{{Cite book
| first1 = Stuart J. | last1 = Russell | author1-link = Stuart J. Russell
