Nice. The Kata might be 7 kyu, but that's a 1 kyu solution.

Ah, List.indexed is really nice, didn't know that one yet.
Better than the |> Seq.mapi ...|> Seq.toList construction that I used to accomplish the same thing.
Thanks for teaching!

Regards,
Maurice

To clarify, the tests expect the solution to open System even if the solution itself does not require it. The tests can use F#'s int64 built-in alias for Int64 or open System.

I don't understand your question:-(

What about built-in int64 type for tests?

I think it is the Codewarrior who has to open System. It is a part of the job, no?

There's a slight issue in the F# version of this kata: the test cases use Int64 as bare type annotations (i.e. without open System or by System.Int64), which means an otherwise valid solution will fail unless it opens System for the tests. Just needs an open System tagging onto the top of the testing code to fix, I think.