Fantastic implementation of a great concept. This is actually quite rare for me, but I have no complaints, and I can't believe I'm saying that about what could technically be called an edutainment game.
Here you've created a set of mechanics which have interesting consequences, and then you've designed a set of puzzles to explore those mechanics. The puzzles slowly introduce you to new concepts that might not be obvious (like the concept of pulling), and then once you learn it, you can now apply it to harder puzzles. I was going to complain, "Why can't I multiply -5x2" for example, until I realized that one mechanic is that there can only be two characters in a box, and -10 has three, so the game stays logically consistent.
It's just good ol' Jon Blow school of puzzle design. He'd probably like this game too, since he does like Sokoban puzzlers with interesting mechanics.
Edit: Actually, one thing I don't understand: On the Conyon, you have at one point 8/(3/3), which collapses into 8/1, but 8/1 doesn't collapse into 8. You're free to push 1 afterward and you need to do so to solve the puzzle. I'm kind of wondering if that results from a bug in the engine or if that's an intentionally programmed inconsistency, or if I'm just misunderstanding the mechanics.