Initial data commit

Task/Sorting-algorithms-Merge-sort/Picat/sorting-algorithms-merge-sort.picat

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+% True if S is a sorted copy of L, using merge sort
+msort([],[]).
+msort([X],[X]).
+msort(U,S) :-
+  split(U, L, R),
+  msort(L, SL),
+  msort(R, SR),
+  merge(SL, SR, S).
+
+% split(LIST,L,R)
+% Alternate elements of LIST in L and R
+split([],[],[]).
+split([X],[X],[]).
+split([L,R|T],[L|LT],[R|RT]) :-
+  split( T, LT, RT ).
+
+% merge( LS, RS, M )
+% Assuming LS and RS are sorted, True if M is the sorted merge of the two
+merge([],RS,RS).
+merge(LS,[],LS).
+merge([L|LS],[R|RS],[L|T]) :-
+    L @=< R,
+    merge(LS,[R|RS],T).
+merge([L|LS],[R|RS],[R|T]) :-
+    L @> R,
+    merge([L|LS],RS,T).