How did you do it so few lines of code? Can you give me some idea of what approach you used?

I implemented polynomial multiplication (by convolution) and subtraction from some code I found on the web and then shrunk it down as much as I could but I have about 500 bytes of code and still haven't implemented the parsing.

I haven't done any polynomial multiplication or subtraction. I used an entirely different approach.

Before v5 I had used direct polynomial division too, but now changed. Maybe my current approach is same to Mark Byers' one.