I realize you may not want to share it, but if you have some sort of resource you could point me at I'd appreciate it, since I also like doing basic arithmetic as a mental game. I view it as similar to the type of casual timekilling that one would do with sudoku or minesweeper, but at least semi-productive in that I'm building mental arithmetic skills. If you feel inclined to share the source so I could run my own instance, I can be reached at my username + google's mail service.
You might like catmath.io. Unless you hate cats.
> Just a reminder: Proofs are usually stuff for a master course.
And that's my criticism. If more people in society cared why something is true, we wouldn't have falsehoods abound all around us that are obviously wrong and logically screamingly incorrect.
Matrix multiplication is an uninportant detail. Modus ponens is what holds everything together. But rarely anybody can handle the latter, nor even has heard of it.
I think these short outburst of calculations are helpful and fun. I for example host a private website for sub/add/mult/div tasks and consider them as same sort of casual gaming, solving these "math problems" in the shortest time possible.
Author's great repo inspired me to add more stuff. I like it.