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
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% \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