let openFiles =
        let file1 = File.OpenText "Integral1.txt"
        let file2 = File.OpenText "Integral2.txt"
        let file3 = File.OpenText "Integral3.txt"
    (file1,file2,file3)
let openAsync = Async.AwaitTask openFiles

let readFiles file =
        let str1 = file.ReadLine()
        let str2 = file.ReadLine()
    (str1, str2)
let readAsync = Async.AwaitTask |> readFiles |> openAsync

let intergrateAsync = Async.AwaitTask |> intergrate |> readAsync
Async.RunSynchronously intergrateAsync
//и где-то раньше функция intergrate расписана