% pt 7
%EX 1
:-dynamic(fib/2).
fib(0,0):-!.
fib(1,1):-!.
fib(N,F):-
    N1 is N-1,
    N2 is N-2,
    fib(N1,F1),
    fib(N2,F2),
    F is F1+F2,
    asserta(fib(N,F):-!).

% EX2
:- dynamic person/1, friend/2, group/2. 
person(jef). 
person(vero). 
person(tom). 
person(christian).
person(pierre). 
friend(vero,tom). 
friend(vero,jef).
friend(vero,christian).
friend(tom,jef).
friend(tom,pierre).
group(g1,[tom,vero,jef]).
group(g2,[vero,christian]). 
group(g3,[pierre]).

remove_person(P):-
   retract(person(P)),
   %forall(friend(P,X),retract(friend(P,X))),
   %forall(friend(X,P),retract(friend(X,P))),
   retractall(friend(P,_)),
   retractall(friend(_,P)),
   forall((group(X,L),member(P,L)),(select(P,L,NL),retract(group(X,L)),asserta(group(X,NL)))).

add_person(P,Friends,Groups):-
    asserta(person(P)),
    forall((member(F,Friends)),(asserta(friend(P,F)))),
    forall((member(G,Groups),group(G,L), not(member(P,L))),(select(P,NL,L),retract(group(G,L)),asserta(group(G,NL)))).

friends(P,X):-
    friend(P,X);friend(X,P).

mediator(P):-
    person(P),
    friends(P,F1),
    friends(P,F2),
    F2 \= F1,
    group(G1,L1),
    member(F1,L1),
    group(G2,L2),
    member(F2,L2),
    G2 \= G1.