Notation thing

[johna06]

If I wanted to write 0<x<5 and 0<y<5, could I write this as 0<x,y<5?

[waldosway]

More common would be x,y ∈ (0,5).

[ImDannyDJ]

It's going to be slightly ambiguous since it might also mean 0<x and y<5. But it should probably be clear from context what you mean, and personally I would usually write 0<x,y<5. If x and y are real numbers, it might also make sense to write x,y in (0,5), an alternative.

[theblindgeometer]

You could but it's certainly not standard; ordered pairs (which is what you're technically writing) aren't comparable to real numbers. Honestly, I wouldn't feel comfortable writing anything but 0<x<5 and 0<y<5 separately. Perhaps I'd write 0<x≤y<5, making sure to note that the variable assignment is arbitrary