%%%%%%%%%%%%%%%%% 1 %%%%%%%%%%%%%%%%%%%%%%%
animal(duck).
animal(cat).
animal(dog).
animal(horse).

swim(duck).
swim(dog).

r(X):-animal(X),swim(X),!,fail.
r(X):-animal(X).

% explain the definition of r(X).
% what are the answers for ?-r(X).
% What happens if we remove ! from the first %rule?
% What kind of ! uses the definition of r? 
%red or green? Explain.

%%%%%%%%%%%%%%%%  2    %%%%%%%%%%%%%%%%%%
% Use the cut fail combination in order to 
% define the predicate no(P) which is true if
% P is false.

%%%%%%%%%%%%%%%%  3   %%%%%%%%%%%%%%%%

%Consider the following friendship relation:
friend(radu, elena).
friend(elena, mihai).
friend(zoe, viorel).

% define, using the cut fail combination the 
%relation unfriend which takes place if it
%is unknown whether X and Y are friends

%%%%%%%%%%%%%%%%%  4    %%%%%%%%%%%%%%%%%%
% What kind of structures can be unified with 
% _, [_], [_,_], [_|_], [X,X|_]

%%%%%%%%%%%%%%%%%  5    %%%%%%%%%%%%%%%%%%%%%%
% A solution to Hanoi's tower
% Move all the disks from axe_1 to axe_2 
% one disk at a time, do not put a greater disk
%on a smaller disk

% one possible answer:
hanoi(N):-move(N,axe_1,axe_2,axe_3).

move(0,_,_,_):-!.
move(N,A,B,C):- M is N-1, move(M,A,C,B), 
                say(A,B), move(M,C,B,A).
say(X,Y):-write([move,one,disk,from,X,to,Y]),nl.



%%%%%%%%%%%%%%%%  6   %%%%%%%%%%%%%%%%%%%%%%%%
%Define a database for the following:
% A day of a week can be Monday, Tuesday, 
% Wednesday, Thursday, Friday, Saturday, Sunday.

% Define relations for:
% next(X,Y) Y is the next day of X
% twodaysafter(X,Y) Y is the second day after X


%%%%%%%%%%%%%%%%%  7   %%%%%%%%%%%%%%%%%%%%%%%
% Consider the following database:
grade(popescu,'LCS',9.0).
grade(popescu,'FP',7.0).
grade(popescu,'LP',10.0).
grade(albu,'Algebra',9.0).
grade(albu,'Management',8.5).

% define a program general_average(Pers,Ga) 
% which computes the general average of the 
% person X. Example:
% ?-general_average(popescu,Ga).
% ?- Ga=8.66666

% Sugestion 1: define a predicate similar to %findall

% Sugestion 2:
% findall(Term,+G,-L)
% computes the list L of all possible instances
% of Term produced by answering to G.
% findall(N,X,grade(popescu,_,N),L).