Is It Math or CS? Or Is It Both?

In November 2024 Communications Vardi's Insights column, "What Is Theoretical Computer Science?", Moshe Vardi raised an interesting point of whether theoretical CS is CS or math. The question is: What is math? Most people outside math consider math as a science of studying abstract structures--just like biology is studying living creatures. However, most mathematicians we know define mathematics not by its subject, but by its level of rigor--mathematics (in contrast, for example, to physics) is making conclusions at the highest level of rigor, that is, proving theorems. Some of these theorems are abstract, some are related to applications. When a researcher proves a theorem about Schroedinger equations, and the result is of interest to physics, of course this is physics, but this is also mathematics--since it is a theorem.