This question was closed for being off topic, and then reopened, presumably for being on topic.
It seems to me that parts of theoretical CS are definitely on topic - e.g. I have read some analysis of algorithms in my number theory books. But do we want to consider questions about
Turing Machines, Computability, etc on topic?
My initial thought is yes, as long as we don't start writing code. Something like lambda calculus seems on topic, and computability and algorithms show up on the list of Hilbert's problems. On the other hand, I could also understand the argument that CS has developed into its own domain. The Area 51 TCS proposal is working its way through commitment, though certainly having a SE dedicated to a topic doesn't mean that we can't discuss it here.
In my mind, this is similar to the question of whether we consider statistics to be part of mathematics or its own discipline.
At any rate, I'd like to hear the community consensus lest I start posting off-topic questions.