The practice version did, but name collisions got too confusing (W and H is fine for width and height, but then I wanted horizontal and vertical velocity...). I

The practice version did, but name collisions got too confusing (W and H is fine for width and height, but then I wanted horizontal and vertical velocity...). I thought it was clearer to give up completely and use the notepad instead. And yes, some optimisations are left as an exercise for the reader.