insert(E,L,R).
insert(1,[],[1]).
insert(2,[3],[2,3]).
insert(5,[4],[4,5]).
insert(6,[8,10],[6,8,10]).
insert(11,[9,14],[9,11,14]).
insert(13,[7,12],[7,12,13]).

insert(X,[],[X]).
insert(X,[Y],[X,Y]) :- X<=Y.
insert(X,[Y],[Y,X]) :- X>Y.

