How to implement all_different in SWI-Prolog

[Shaitan00]

I am writing a swi-prolog program to solve a sudoku puzzle, the program is working perfectly when using the built-in "all_different" predicate but I was now instructed to actually write my own and not take advantage of the available function. Therefore I am attempting to write my own customized version "alldifferent(L):-" that will achieve the same results.

  alldifferent([A1,B1,C1,D1]), 
  alldifferent([A2,B2,C2,D2]), 
  alldifferent([A3,B3,C3,D3]), 
  alldifferent([A4,B4,C4,D4]), 
  ... 

  alldifferent([_]).		% Base Case
  alldifferent(H,T) :- H\=T.	% Compare Head and Tail
  alldifferent([H|T]) :- alldifferent(H,T), alldifferent(T).
[/oOde] 

As you can see I pass in a list of 4 variables and I need to ensure that none of them are the same. I've been trying to implement this for a while now and can't seem to figure it out (I've written my current attempt) - I was wondering if anyone could provide some help. MY current attempt doesn't work (not sure how you can compare the head of a list [H] with the tail [T] and am doubtful about my base-case.

Any hints would be greatly appreciated. 
Thanks,

 

[4tangent]

I think your base case is OK
The next line needs squared brackets to make it a list format.
The third line - you should not mix lists [H|T] with non-lists H,T. The third line also needs reworking. You could look at using the "member" predicate to look for duplication.
Cheers
John