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Math: $u=\underset{0}{\overset{w}{\int }}f(a,u)dt$

Ugly stuff: $a⟹b$

Displayed equation:

$\begin{array}{rl}x& =1\\ y& =2\end{array}$

AMS Math: <amsmath> u = \int_0^h f(a,u) dt </amsmath>

Interwiki link: FBS wiki