Hello world.

This is a display style equation:

$$ p(x) = \int p(x,y) dy $$

This is an equation $p(x)=f(x)$ that is inline.

```
Code block
Line 1
Line 2
Line 3
```

% \f is defined as #1f(#2) using the macro \f\relax{x} = \int_{-\infty}^\infty \f\hat\xi,e^{2 \pi i \xi x} ,d\xi