Math symbol for positive correlation

Question

I want to represent in a math formula the positive correlation between two variables. For instance, how could you express the positive correlation between $x$ and $y$, where $x$ is the amount of minutes a student studies for a test, and $y$, the grade obtained on the test?

Answer 1

I see two possible options.

Assume $y = f(x)$ then you can say that $y$ is positively correlated with $x$ if $f'(x) > 0$.

Without resorting to a $f$, you can equivalently write $corr(x, y) > 0$.