View sourcecode

mergesort([],[]). % special case
mergesort([A],[A]).
mergesort([A,B|R],S) :-
   split([A,B|R],L1,L2),
   mergesort(L1,S1),
   mergesort(L2,S2),
   merge(S1,S2,S).

split([],[],[]).
split([A],[A],[]).
split([A,B|R],[A|Ra],[B|Rb]) :-  split(R,Ra,Rb).