Prolog Lab 5 - Prob 5

Repeat(X, N, Reps, Reps_back) :-
    (   succ(N0, N)
    ->  Reps = [X|Reps0],
        repeat(X, N0, Reps0, Reps_back)
    ;   Reps = Reps_back
    ).

decode(Encoded, Decoded) :-
    decode_1(Encoded, Decoded, []).

decode_1([], Decoded, Decoded).
decode_1([[X,N]|XNs], Decoded, Decoded_back) :-
    repeat(X, N, Decoded, Decoded_rest),
    decode_1(XNs, Decoded_rest, Decoded_back).