There is a reset collectible based on basic math and even mention how to do it in the How to play.
But it's basic math. If you multiply anything by 0, you get 0. ;)
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Ah yes, there is not any gameover at all at the moment. Although I've considered adding some enemy fish at some point and maybe something more negative if the player tries to divide by 0. Currently just makes a sound for that.
I will be adding a save mechanic into the game once we can edit the games. That way you can keep aiming for the bigger numbers.