`map4` about fsharpaux HOT 2 OPEN

// Working with 4 enumerable collections at once without proper functions is tedious.
// FSharp.Core.Collections provides mapping functions for one, two, and three collections, yet a mapping function for four is missing.
let map4 f (a1: _[]) (a2: _[]) (a3: _[]) (a4: _[]) =
    Array.init (Array.length a1) (fun i -> f a1.[i] a2.[i] a3.[i] a4.[i])

// Working with 5 enumerable collections simultaneously without proper functions is a nightmare.
// FSharp.Core.Collections' mapping functions for one through four collections aren't enough to make this task any easier.
let map5 f (a1: _[]) (a2: _[]) (a3: _[]) (a4: _[]) (a5: _[]) =
    Array.init (Array.length a1) (fun i -> f a1.[i] a2.[i] a3.[i] a4.[i] a5.[i])

// Attempting to work with 6 enumerable collections without a proper function is like trying to juggle six flaming swords.
// We need a mapping function for six collections, and we need it yesterday!
let map6 f (a1: _[]) (a2: _[]) (a3: _[]) (a4: _[]) (a5: _[]) (a6: _[]) =
    Array.init (Array.length a1) (fun i -> f a1.[i] a2.[i] a3.[i] a4.[i] a5.[i] a6.[i])

// Working with 7 enumerable collections at once is like trying to solve a Rubik's Cube blindfolded.
// We need a mapping function for seven collections, and we need it now!
let map7 f (a1: _[]) (a2: _[]) (a3: _[]) (a4: _[]) (a5: _[]) (a6: _[]) (a7: _[]) =
    Array.init (Array.length a1) (fun i -> f a1.[i] a2.[i] a3.[i] a4.[i] a5.[i] a6.[i] a7.[i])

// Working with 8 enumerable collections at once is like trying to herd eight cats.
// FSharp.Core.Collections' mapping functions for one through seven collections are no match for this task.
// We need a mapping function for eight collections, and we need it fast!
let map8 f (a1: _[]) (a2: _[]) (a3: _[]) (a4: _[]) (a5: _[]) (a6: _[]) (a7: _[]) (a8: _[]) =
    Array.init (Array.length a1) (fun i -> f a1.[i] a2.[i] a3.[i] a4.[i] a5.[i] a6.[i] a7.[i] a8.[i])

// Working with 9 enumerable collections at once is like trying to perform brain surgery while skydiving.
// FSharp.Core.Collections' mapping functions for one through eight collections are simply not enough to make this task manageable.
// We need a mapping function for nine collections, and we need it yesterday!
let map9 f (a1: _[]) (a2: _[]) (a3: _[]) (a4: _[]) (a5: _[])