let task4 (words: string seq) : Text =
    let wordsCount = words |> Seq.countBy id
    let dict =  wordsCount
                |> Seq.filter (fun x -> (snd x) > 5)
                |> Seq.map (fst)
                |> Seq.toArray
    let text =  words
                |> Seq.map (fun x -> try Id(Array.findIndex (fun y -> y = x) dict) with | :? System.Collections.Generic.KeyNotFoundException -> String(x))
    (text, dict)