What is your favorite theorem ?

I have 2 theorems which trigger my love of Math :

**Chinese Remainder Theorem:**韩信点兵, named after a 200 BCE Han dynasty genius general**Han Xin （韩信）**who applied this modern “Modular Arithmetic” in battle fields.**Fermat’s Last Theorem**：The Math “prank” initiated by the 17CE amateur Mathematician Pierre de Fermat kept the world busy for 380 years until 1974 proved by Andrew Wiles.

**Note 1**: Lycée Pierre de Fermat (Classe Préparatoire) happens to be my ** alma mater** named after this great Mathematician born in the same southern France “Airbus City” Toulouse.

**Note 2**: His another Fermat’s Little Theorem is used in modern computer cryptography.