I just want to make sure that I don't get in trouble with Stack Exchange for posting this image.
I have written a paper that is a specific rebuttal to the proof contained in the image. I didn't even need to copy the whole proof, I skipped the last page. To the best of my knowledge this is allowed as "fair use" on the basis that its purpose is academic scholarship and the fact that a rebuttal of a proof is very much transformative relative to the original proof.
Linz, Peter 1990. An Introduction to Formal Languages and Automata. Lexington/Toronto: D. C. Heath and Company (317-319).