This is an old revision of the document!
let's see first “play” and “ground”. ground=worldwild. that is play?
<latex>
\frac{3}{4 \pi} \sqrt{4 \cdot x^2 12}\\ \lim_{n \to \infty} \sum_{k=1}^n \frac{1}{k^2} = \frac{\pi^2}{6} e^{i \pi} + 1 = 0 \\
</latex>