One, two, three, four // Come in, please, and shut the door

          It is a  fun poem for children. You can learn English and Mathematics at the same time.

          The following example contains ONLY math... And some gold!

$$\arctan \frac{1}{2}+\arctan \frac{3}{4}=2\arctan \frac{1}{\varphi}$$

Enjoy!