[N,M,X,Y,L]

le(0,Y) -> true.
le(s(X),0) -> false.
le(s(X),s(Y)) -> le(X,Y).
app(nil,Y) ->  Y.
app(cons(N,L),Y) -> cons(N,app(L,Y)).
low(N,nil) -> nil.
low(N, cons(M,L)) -> iflow(le(M,N),N,cons(M,L)).
iflow(true, N, cons(M,L)) -> cons(M,low(N,L)).
iflow(false, N, cons(M,L)) -> low(N,L).
high(N,nil) -> nil.
high(N, cons(M,L)) -> ifhigh(le(M,N),N,cons(M,L)).
ifhigh(true, N, cons(M,L)) -> high(N,L).
ifhigh(false, N, cons(M,L)) -> cons(M,high(N,L)).
quicksort(nil) -> nil.
quicksort(cons(N,L)) -> app(quicksort(low(N,L)),cons(N,quicksort(high(N,L)))).

