; Node-Based, Bi-Directional Inference
;
; Define arcs.
(define member class object property)
;
; for every p
;  if p is a man or p is a woman then p is mortal and p is a rational animal.
(describe (assert forall $p
		     ant ((build member *p class man)
			  (build member *p class woman))
		      cq ((build object *p property mortal)
			  (build member *p class "rational animal"))))
;
; Socrates is a man.
(describe (assert member Socrates class man))
;
; Backward inference looks for all possible antecedents,
; but ignores other possible conclusions.
; Is Socrates mortal?
(describe (deduce object Socrates property mortal))
;
; Forward inference yields all possible conclusions.
; Ada is a woman!
(describe (add member Ada class woman))
;
; Backward inference to establish the context that what we are
; interested in is whether anyone is a rational animal.
; Who is a rational animal?
(describe (deduce member *p class "rational animal"))
;
; Now, when we add information, conclusions irrelevant to the context
; are not drawn.
; Turing is a man!
(describe (add member Turing class man))