What does the ぬ in 詰まぬ mean?

Question

I encountered a Shogi saying:

三桂あって詰まぬこと無し

And I'm pretty confused about the ぬ there. If it was る I'd expect the meaning to be something like:
"If you have 3 knights, you can't be mated"

But looking at it's explanation here and here it looks like they are talking about mating (attacking) and not getting mated (defending).

Well, while typing this I suddenly realized I can just search google for ぬ instead of る, so I'll guess I'll be answering my own question as I was encouraged to do on other StackExchange sites.

Answer 1

The ぬ is a classical form of ない. While it's not often used you will probably still encounter it in some situations (proverbs are a great example).

In this situtation 詰まぬ=詰まない meaning "not being mated" so a translation for the proverb may be:

With 3 knights, there's always a mate (no such thing as being unmatable?)