Class PN-ARROW

Subclass-Of: Diagram-object
Axioms:
(=> (Pn-Arrow ?Self)
    (And (Exists (?A) (And (Part-Of ?Self ?A) (Petri-Net ?A)))
         (Exists (?B)
                 (And (Represents ?Self ?B)
                      (Time-Span ?B)
                      (Exists (?C)
                              (And (Precedes ?B ?C) (*Phase ?C)))
                      (Forall (?C ?D)
                              (=> (And (Precedes ?B ?C)
                                       (Precedes ?B ?D))
                                  (= ?C ?D)))))))