let rec combinations n l =
        match n, l with
        | 0, _ -> [[]]
        | _, [] -> []
        | k, (x::xs) -> List.map ((@) [x]) (combinations (k-1) xs) @ combinations k xs
 
let rec cross acc xs = 
        match xs with 
        | h :: t -> cross ([ for e in t -> h, e] @ acc) t
        | [] -> acc
 
let solve n (lst : int list) = 
        [ for e in 1..n -> combinations e lst ]
        |> Seq.collect id 
        |> Seq.groupBy List.sum
        |> Seq.filter (fun (_,e) -> Seq.length e > 1)
        |> Seq.collect (snd >> Seq.toList >> cross [])
        |> Seq.toList
 
solve 6 [1..12] 
|> List.rev |> List.head
|> printfn "%A"

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