%test
fact(0,1).
fact(N,A) :- N1 is N-1,fact(N1,A1),A is N*A1.

my_member(X, [X|_]).
my_member(X, [_|Y]) :- my_member(X, Y).

likes(kim,robin).
likes(sandy,lee).
likes(sandy,kim).
likes(robin,cats).
likes(sandy,X) :- likes(X,cats).
likes(kim,X) :- likes(X,lee),likes(X,kim).
likes(X,X).


tarai(X,Y,Z,A) :- A is elx_tarai(X,Y,Z).

ack(M,N,A) :- A is elx_ack(M,N).

qsort([],[]).
qsort([X],[X]).
qsort([X|Xs],Y) :-
  part(X,Xs,S,L),qsort(S,S1),qsort(L,L1),append(S1,L1,Y).

pqsort([],[]).
pqsort([X],[X]).
pqsort([X|Xs],Y) :-
  part(X,Xs,S,L),parallel(pqsort(S,S1),pqsort(L,L1)),append(S1,L1,Y).

fib(0,0).
fib(1,1).
fib(N,A) :-
  N1 is N-1,N2 is N-2,
  fib(N1,A1),fib(N2,A2),A is A1+A2.

pfib(0,0).
pfib(1,1).
pfib(N,A) :-
  N1 is N-1,N2 is N-2,
  parallel(pfib(N1,A1),pfib(N2,A2)),A is A1+A2.

part(A,[],     [A],[]).
part(A,[X|Xs],S0,L) :- A>=X,S0=[X|S], part(A,Xs,S,L).
part(A,[X|Xs],S,L0) :- A < X,L0=[X|L], part(A,Xs,S,L).

my_append([], Z, Z).
my_append([W|X1], Y, [W|Z1]) :-
  my_append(X1, Y, Z1).


!elixir
def ack(0, n), do: n + 1
def ack(m, 0), do: ack(m - 1, 1)
def ack(m, n), do: ack(m - 1, ack(m, n - 1))

def tarai(x, y, z) do
  cond do
    x <= y -> y
    true -> tarai(tarai(x - 1, y, z), tarai(y - 1, z, x), tarai(z - 1, x, y))
  end
end