% A sample database.  

% Percent-sign ('%') marks comments to end-of-line.

% FACTS
male(abe).
male(homer).
male(bart).

parent(jackie,marge).

parent(abe,homer).
parent(mona,homer).

parent(homer,bart).
parent(marge,bart).

parent(homer,lisa).
parent(marge,lisa).

parent(bart,bartJr).
parent(bart,cowabunga).
parent(bartJr,bartJrII).
   
      
% RULES
father(Dad, Child) :- parent(Dad, Child),   male(Dad). 

% Dad is the father of Child 
%  if Dad is the parent of Child and Dad is male

% Use meaningful variable names.  Cf.
%       father(X, Y) :- parent(X, Y), male(X). 
% (You can use generic var names when representing a generic input.)
     
 
%    ":-" read as "if"
%    ","  read as "and"



%%%% Define grandparent:
%%%% (What is the def'n in English, for "Old is a grandparent of Yng"?)
%%%%

%%%% Define grandfather:

%%%% Define "ancestor":
anc(P,P).
anc(P1,P2) :- parent(P1,Middle), anc(Middle,P2).

cousin(X,Y) :- parent(P,X), parent(P,Y).   % siblings are 0th-cousins.
cousin(X,Y) :- parent(PX,X), parent(PY,Y), cousin(PX,PY).





%%%% Cousin:

%%%% Digress, in English:
%%%%  cousin, 2nd cousin, 3rd cousin;
%%%%     nth cousin m times removed.

%%%% nthCousin: