Prolog difference list - mergesort -

I must write a predicate that will divide a list into two lists (on half):

  Partial (XY, XZ, ZY): - halve_pom (XY, XY, Z),! Halve_pom (Z-Y, Y-Y, Z) Halve_pom ([_ | A] -Y, [_, _ | B] -Y, Z): - halve_pom (A-Y, B-Y, Z).   
 It was easy, but now I have to type the algorithm which will merge - I have no idea. This algorithm should use the difference list.  
 Please help. No, it was not "easy" because it does not work, unfortunately    
 
 
 Halva ([1,2,3] - [], A, B)  does not work;  halve_pom ([1,2,3] - [], A, B)  does not work either. Apart from this, it is not clear what splashing schemes you like,  [1,2,3,4,5,6,7] - & gt; ([1,3,5,7], [2,4,6])  or  - & gt; ([1,2,3,4], [5,6,7]) .  
 If your  half  works in the works, then you have to define  merge  to do whatever you have left, which are two parts of the list Mergeresort (A, S): - Halva (A, B - [], C- []), MergeRort (B, SB), Merger (C, SC), Merge (SB, Scheduled Castes, S []).   
 Note that you might call it with the normal list  A , that is,  half  predicate your first argument to a general list (I.e. not the difference list).  
 Also see.  '-'  is unnecessary; Instead, two components of it should be used as two different arguments of an ingenious.  
 
 Therefore, a method of code is  halve   
  half ([A, B | C], [A | X] -JX, [BY] - Jiayu): - Half (C, X-ZX, Wi-YE). Half ([One], [X | X] -X, Y-Y). Half ([], X-X, Y-Y).   
 The same approach can be used for code  merge :  
  merge (SB, SC, SZ): - SB = [A | B], SC = [C | D], A = & lt; C, S = [A | T], merge (B, SC, TZ). Merge (SB, SC, S-Z): - SB = [A | B], SC = [C | D], A & gt; C, ..., .... Merge (SB, SC, S-Z): - SB = [A | B], SC = [], ..., .... Merge (SB, SC, S-Z): - SB = [], SC = [C | D], S = [C | T], .... Merge ([], [], Z-Z).