The following problem is presented in Wirth1976:
I married a widow (let’s call her W )who has a grown-up daughter (call her D). My father (F), who visited us often, fell in love with my step-daughter and married her. Hence my father became my son-in-law and my step-daughter became my mother. Some months later, my wife gave birth to a son (S1),who became the brother-in-law of my father, as well as my uncle. The wife of my father, that is, my step-daughter, also had a son (S2).
Represent this situation using the predicates defined in the previous exercise,verify its conclusions, and prove that the narrator of this tale is his own grandfather.
Code:
(<- (parent ?p ?c) (married ?p ?w) (child ?c ?w))
(<- (parent ?p ?c) (married ?h ?p) (child ?c ?w))
(<- (son-in-law ?s ?p) (parent ?p ?w) (married ?s ?w))
(<- (male I))
(<- (male F))
(<- (male S1))
(<- (male S2))
(c- (female W))
(<- (female D))
(<- (married I W))
(<- (married F D))
(<- (child D W))
(<- (child I F))
(<- (child S1 I))
(<- (child S2 F))
Tests:
(?- (son-in-lawFI))
(?- (mother D I))
(?- (uncle S1 I))
(?- (grandfather I I ) )