Things that are "computer science" but I contend are not mathematics: programming language design and implementation, operating system design and implementation, computer architecture and networking.
All of these things depend on math. But they go beyond the scope of math because they deal with the realities of designing and building systems for computation. Physics also relies on math, but I've never seen anyone make the reductionist statement "Physics is a branch of mathematics."
> programming language design [...] All of these things depend on math.
Really? I'm currently designing and implementing a programming language, and I haven't (consciously, at least) used any maths concepts more complex than arithmetic.
Some aspects of programming languages are very math heavy - things like type theory and lambda calculus. It's accurate to say some of the field of programming language design and implementation depends on math. Hence, I'm willing to say the field aggregate has that dependence, even if some other parts of the field do not have an explicit dependence.
All of these things depend on math. But they go beyond the scope of math because they deal with the realities of designing and building systems for computation. Physics also relies on math, but I've never seen anyone make the reductionist statement "Physics is a branch of mathematics."