I love math. Just after the high-school entrance ceremony, I meet a beautiful girl: Milka. Milka is a mathematical genius. She shows me many math and many elegant solutions. Milka and I spend a long time discussing math in the school library. One year later, I meet another mathematical girl: Tetra. Tetra is one year younger than me, and asks me to teach her math. While I teach her, she begins to understand math and gradually to love its elegance. The third series is about logic puzzles, Peano arithmetic, epsilon-delta, Cantor's diagonal argument, Hilbert's program and Gödel's Incompleteness Theorems.