This is another drawing from Tatchee, Angry Bird characters surrounded by calculus formula. How did this come about?
One time Tatchee was bugging me to get him a piece of paper for him to draw. There was nothing available. So I reluctantly handed him my real calculus notes, which I was carrying for study. I asked him to draw on the margin. When I got it back I found it adorned with Angry Birds characters.
The original of the notes was on my computer. Usually I carry the paper around and scribble on it. It gets worn out quickly. Then I would update the notes on my computer and print a new one. But this one is so cute I can't throw it away. It ended up become my keepsake.