[F#][оптимизация] возможно ли что-то сделать

let a = [1..10000]
let b = [1..10000]

let intersectionCollect f l1 l2 =
    l1 |> List.collect (fun el1 ->
                            l2 |> List.collect (fun el2 ->
                                                    match f el1 el2 with
                                                    | Some(res) -> [res]
                                                    | None -> []))

intersectionCollect (fun a b -> if (a = b) then Some(a,b) else None) a b
(*Real: 00:00:10.020, CPU: 00:00:09.562, GC gen0: 3, gen1: 1, gen2: 0*)

let intersectionCollect2 f l1 l2 =
    l1 |> List.fold 
            (fun acc el1 ->
                (l2 |> List.fold 
                        (fun acc el2 ->
                            match f el1 el2 with
                            | Some(res) -> res :: acc
                            | None -> acc) 
                        []) :: acc) 
            [] 

intersectionCollect2 (fun a b -> if (a = b) then Some(a,b) else None) a b
(*Real: 00:00:04.783, CPU: 00:00:04.718, GC gen0: 2, gen1: 0, gen2: 0*)

let a = [1..10000]
let b = [1..10000]

let intersectionCollect f l1 l2 =
    l1 |> List.collect (fun el1 ->
                            l2 |> List.collect (fun el2 ->
                                                    match f el1 el2 with
                                                    | Some(res) -> [res]
                                                    | None -> []))

intersectionCollect (fun a b -> if (a = b) then Some(a,b) else None) a b
(*Real: 00:00:09.516, CPU: 00:00:09.390, GC gen0: 4, gen1: 1, gen2: 0*)

let intersectionCollect2 f l1 l2 =
    l1 |> List.fold 
            (fun acc el1 ->
                (l2 |> List.fold 
                        (fun acc el2 ->
                            match f el1 el2 with
                            | Some(res) -> res :: acc
                            | None -> acc) 
                        []) @ acc) 
            [] 

intersectionCollect2 (fun a b -> if (a = b) then Some(a,b) else None) a b
(*Real: 00:00:04.918, CPU: 00:00:04.859, GC gen0: 3, gen1: 0, gen2: 0*)

let rec intersectionCollect2 f l1 l2 = [
    for el1 in l1 do
        for el2 in l2 do
            match f el1 el2 with
            | Some(res) -> yield res
            | None -> ()
]

let rec intersectionCollect3 f l1 l2 = 
    let els = new List<_>()
    for el1 in l1 do
        for el2 in l2 do
            match f el1 el2 with
            | Some(res) -> els.Add(res)
            | None -> ()
    els |> Seq.toList

(*Real: 00:00:20.524, CPU: 00:00:20.515, GC gen0: 10, gen1: 1, gen2: 0*)

(*Real: 00:00:06.143, CPU: 00:00:06.078, GC gen0: 3, gen1: 1, gen2: 0*)