Consider a database of facts that describe parent relationships as well as gende

Question

Consider a database of facts that describe parent relationships as well as gender relationships. The predicate parent(john,ann) is interpreted as: "John is a parent of Ann". The predicate male(john) is interpreted as: "John is a man". The predicate female(ann) is interpreted as: "Ann is a woman". So an example database of facts is:

parent(john,ann).
parent(jim,john).
parent(jim,keith).
parent(mary,ann).
parent(mary,sylvia).
parent(brian,sylvia).
male(keith).
male(jim).
female(sylvia).
female(ann).
male(brian).

Note that some things are not specified in the database above (e.g., male(john)).

Write a Prolog predicate uncle(X,Y) that is true if X is Y's uncle. Note that we are not considering uncles "by marriage", meaning that for X to be Y's uncle the two must be related by blood. Sample tests for your code (user input is in red):

?- uncle(keith,ann).
Yes

?- uncle(ann,mary).
No

?- uncle(keith,X).
X = ann ;
No

?- uncle(john,ann).
No

?- uncle(X,Y).
X = keith
Y = ann ;
No

Also, write a Prolog predicate halfsister(X,Y) that is true if X is Y's half-sister. Sample test for your code (user input is in red):

?- halfsister(ann,sylvia).
Yes

?- halfsister(X,sylvia).
X=ann ;
No

?- halfsister(X,Y).
X=ann
X=sylvia ;

X=sylvia
X=ann ;
No

Explanation / Answer

%%X is an uncle of Y if and only if X is a man, there exists some person Z who is

%%a parent of Y and X and Z have a common parent

uncle(X,Y) :- parent(Z,Y),parent(A,X),parent(A,Z),male(X).

half(B,C,X,Y):-parent(B,X),parent(C,Y),not(B=C),!.

%% The above rule is added to prevent backtracking (using ! or cut)

%% and producing same results again and again

%%X is a half sister of Y if and only if X is a woman, X and Y have one same parent

%%and one different parent

halfsister(X,Y):- female(X),parent(A,X),parent(A,Y),not(X=Y),half(B,C,X,Y).

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