;; QA4 Blocks World Example
;; Based on: "QA4: A Procedural Calculus for Intuitive Reasoning"
;; Rulifson, Derksen, Waldinger, SRI Technical Note 73 (1973)

; Define the initial state of blocks world
(ASSERT (ON A TABLE))
(ASSERT (ON B TABLE))
(ASSERT (ON C A))
(ASSERT (CLEAR C))
(ASSERT (CLEAR B))

; Operator: Put block X on top of block Y
(CONSEQUENT PUTON (X Y)
  (PREREQUISITES
    ((CLEAR X))
    ((ACHIEVE (CLEAR Y))))
  (DELETIONS
    ((ON X (? W)))
    ((CLEAR Y)))
  (ADDITIONS
    ((ON X Y))
    ((CLEAR (? W)))))

; Goal: Achieve a specific configuration
(GOAL (ACHIEVE (ON A B)))
(GOAL (ACHIEVE (ON B C)))