opencog-atomspace / tests / query / buggy-crime.scm

; Example taken from "Artificial Intelligence - A Modern Approach"

; "The law says that it is a crime for an American to sell weapons to hostile
; nations. The country Nono, an enemy of America, has some missiles, and all
; of its missiles were sold to it by ColonelWest, who is American."

; "... it is a crime for an American to sell weapons to hostile nations":
; American(x) ∧ Weapon(y) ∧ Sells(x, y, z) ∧ Hostile(z) ⇒ Criminal (x).
(RuleLink
    (AndLink
        (InheritanceLink
            (VariableNode "$x")
            (ConceptNode "American"))
        (InheritanceLink
            (VariableNode "$y")
            (ConceptNode "weapon"))
        (EvaluationLink
            (PredicateNode "sell")
            (ListLink
                (VariableNode "$x")
                (VariableNode "$y")
                (VariableNode "$z")))
        (InheritanceLink
            (VariableNode "$z")
            (ConceptNode "hostile")))
    (InheritanceLink
        (VariableNode "$x")
        (ConceptNode "criminal")))


; The pattern specified here is buggy: its an invalid pattern
; because the variable $x never appears unquoted in the pattern.
; In fact, the pattern has no variables in it at all, since any
; quoted variable is not a variable, but is a constant.
(define (query_rule_bad)
    (QueryLink
        (VariableNode "$x")
        (InheritanceLink
            (QuoteLink
                (VariableNode "$x")
            )
            (ConceptNode "criminal")
        )
        (InheritanceLink
            (VariableNode "$x")
            (ConceptNode "criminal")
        )
    )
)


; This is pattern is valid, and should be able to match 
; two clauses in the above:  $zzz can be grounded by 
; (VariableNode "$x") and it can be grounded by 
; (QuoteLink (VariableNode "$x"))
; ... err right, except that (QuoteLink (VariableNode "$x"))
; is not actually in the atomspace, because query_rule_bad
; cannot be added to the atomspace: it will throw an exception
; when the add is attempted. And thus, the atomspace does not
; actually contain (QuoteLink (VariableNode "$x")) in it...
;
; Conclude: the below will find only one grounding!
(define query_rule_good
    (CollectionOf
    (QueryLink
        (VariableNode "$zzz")
        (InheritanceLink
            (VariableNode "$zzz")
            (ConceptNode "criminal")
        )
        (InheritanceLink
            (VariableNode "$zzz")
            (ConceptNode "criminal")
        )
    )
    )
)