#lang datalog/sexp
; path test from Chen & Warren
(! (edge a b))
(! (edge b c))
(! (edge c d))
(! (edge d a))
(! (:- (path X Y)
       (edge X Y)))
(! (:- (path X Y)
       (edge X Z)
       (path Z Y)))
(! (:- (path X Y)
       (path X Z)
       (edge Z Y)))
(? (path X Y))
