Nested if-else in Prolog?

My Prolog code is not working

maxdis(A, B, C, D) :-
(   abs(A - B) >= abs(A - C) ->
    D is abs(A - B),
    write(D),
    (   abs(B - C) >= abs(A - B) ->
        D is abs(B - C),
        write(D)
    ;   write(D)
    )
;   D is abs(A - C),
    write(D)
).

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result:
maxdis(0,12,-8,X).
12 
no

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Expected result: 20