shuffle([],      X,          X).
shuffle(X,      [],          X).
shuffle([X|Y], Z,         [X|W]):-shuffle(Y,Z,W),Z \= [].
shuffle(Y,       [X|Z],   [X|W]):-shuffle(Y,Z,W),Y \= [].

order([]).
order([X]).
order([X,Y|Z]):-X <= Y, order([Y|Z]).

merge(X,Y,Z):-shuffle(X,Y,Z),order(Z).

:-print('shuffle, order and merge loaded').