A little sudoku-like app for helping first-graders practice addition

merge quasi-bug

This doesn't cause problems in this particular fork, but it's still muddy that Mode can be nil.

Created by  akkartik  on December 7, 2023
CC6INQTAHED2NO7Q34KIWHFHDKG3AL427DS2PY4MYJNX52PBQVTAC
Change contents