ProofWiki:Sandbox

$$ \begin{matrix} z       & = & a \\ f(x,y,z) & = & x + y + z \end{matrix} $$

$$ \begin{cases} 42 \\ 24 \end{cases} $$

$$ \begin{array}{lll} 3+4 & = & 4+3\\ & = & 7 \end{array} $$

$$\therefore$$

$$ \overbrace{\underbrace{ \pi = 3.14159265\ldots }_{bottom}}^{top} $$