Challenge 203.1: Solution in SWI Prolog

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+#!/usr/bin/env swipl
+% -*- prolog -*-
+
+:-initialization(main).
+
+use_module(library(lists)).
+use_module(library(aggregate)).
+
+special(List, [A, B, C, D]) :-
+    A < B,
+    B < C,
+    C < D,
+    nth1(A, List, ElemA),
+    nth1(B, List, ElemB),
+    nth1(C, List, ElemC),
+    nth1(D, List, ElemD),
+    ElemA + ElemB + ElemC =:= ElemD.
+
+combination(0, _, []).
+combination(N, [X|T], [X|Comb]) :-
+    N > 0,
+    N1 is N - 1,
+    combination(N1, T, Comb).
+combination(N, [_|T], Comb) :-
+    N > 0,
+    combination(N, T, Comb).
+
+indexes([], []).
+indexes(List, Indexes) :-
+    length(List, Len),
+    numlist(1, Len, I),
+    combination(4, I, ICombo),
+    permutation(ICombo, Indexes).
+
+find_special(Nums) :-
+    indexes(Nums, Indexes),
+    special(Nums, Indexes).
+
+solution(Nums, Count) :-
+    aggregate_all(count, find_special(Nums), Count).
+
+main :-
+    solution([1,2,3,6], Ex1),
+    solution([1,1,1,3,5], Ex2),
+    solution([3,3,6,4,5], Ex3),
+    format('Example 1: ~w~n', [Ex1]),
+    format('Example 2: ~w~n', [Ex2]),
+    format('Example 3: ~w~n', [Ex3]),
+    halt.