Nice - I had some trouble with it, i.e. the combinations listed in the guide do not necessarily produce what they say they will, or at least don't appear to? Perhaps they can't produce things if the places they would produce them are filled, but it would be nice to see a grid legend instead of a simple equation legend if that's the caes (since positioning is of utmost importance).
Overall seems fun though. Very cute. Music is always nice to have. I did want to say that the font became difficult to read when it shrank due to having more text in a particular dialogue line. I also had a bit of trouble because the interface kept only accepting different input... i.e. click / space don't do anything on the game start screen where it kindly says to press enter, but then although several keys are given as commands, the mouse is also required in the puzzle itself. (It would be really nice to have some keyboard inputs to replace the clicks so then it could be keyboard-only instead of hybrid.)
Definitely don't want to sound harsh though, great job! ^_^