Cool

It's a really nice concept, but can use more work.
There are some annoying glitches, specially when trying to positionate an operator and it places itself in the top left space, no matter where you were trying to put it.
There could be shortkeys for most things, but the one I missed most was one for deleting the current operator, also a restart button for clearing the level would be really appreciated.
The objective of the level could always show, that way, it would be a lot easier than clicking info to see it, to make sure you're thinking accordingly.
Can't you also make the pop-up menu for configuration of the operators in the right (side) menu? So instead of popping up you'd be able to edit it directly on the right menu when you've selected the operator.
The difficulty level scales too fast, and is non-linear (I still am not able to solve lv 7, and didn't tried lv 10 yet, but I solved all the others), more in-between levels and better planning of the order would solve this (and a skip level button and a level select screen, with a limit to how many levels you can skip, resetting when you finish a level you left behind).
Instead of a few very easy levels, you could make a tutorial, covering all the functions of the game, as well as the use of operators. (I'm used to the modulo operator, but I'm pretty sure not everyone is, for instance; and it took me a while to understand exactly what you meant for the things you've written in the instructions in-game). Also, in the level with the + and - operators, it pretty much defeats the point of learning how to use them if they'll be adjusted to 0 as default.
After adjusting those topics, I'm pretty sure your game would get a way better score if you also expanded the number of levels.
Variation of the music is also something to look for (you can get plenty of nice musics here in the portal, all you need to do is credit the autors), so it doesn't get annoying after a while.
Good job, anyway.