Monthly Archives: August 2013

I hate the Pumping Lemma

Posted on 2013-08-18 by Robin Houston

I hate the Pumping Lemma for regular languages. It’s a complicated way to express an idea that is fundamentally very simple, and it isn’t even a very good way to prove that a language is not regular. Here it is, … Continue reading →

Posted in chatter | 45 Comments

The algebra of Unix command substitution

Posted on 2013-08-16 by Robin Houston

Shadab Ahmed raised an interesting question. Open a Unix command shell, type : ‘!!’ and press return. Then type : “!!” ‘!!’ and press return. Now repeat the following a few times: press the up arrow, and press return.

Posted in Mathematics | 6 Comments