Which of these mathematical English sentences is correct?

Question

I am very poor at English.

I want to know which of these sentences is correct.

1. If $f(x, y)$ is a $C^2$ function, then $\frac{\partial^2 f}{\partial x \partial y}$ and $\frac{\partial^2 f}{\partial y \partial x}$ are the same function.

2. If $f(x, y)$ is a $C^2$ function, then $\frac{\partial^2 f}{\partial x \partial y}$ and $\frac{\partial^2 f}{\partial y \partial x}$ are the same functions.