I was wondering how one would go about proving a language is Not Regular without using the traditional pumping lemma contradiction.
$$L = \{ 1^k 0^n 1^n 0^k \mid k \geq 0, n \geq 0\}$$
I've seen a method before where you would Intersect this language with another one and show that the result is Not regular. But I'm lost on what to intersect it with.