$f(x)=\int_{-\infty}^x~e^{-t^2}dt$

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$\frac{1}{\displaystyle 1+ \frac{1}{\displaystyle 2+ \frac{1}{\displaystyle 3+x}}} + \frac{1}{1+\frac{1}{2+\frac{1}{3+x}}}$

$\begin{eqnarray}
 y &=& x^4 + 4      \nonumber \\
   &=& (x^2+2)^2 -4x^2 \nonumber \\
   &\le&(x^2+2)^2
\end{eqnarray}$
------------------------------------

$F(x,y)=0
\left| \begin{array}{ccc}
  F''_{xx} & F''_{xy} &  F'_x \\
  F''_{yx} & F''_{yy} &  F'_y \\
  F'_x     & F'_y     & 0 
  \end{array}\right| = 0$
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$\underbrace{a+\overbrace{b+\cdots}^{{}=t}+z}
_{\mathrm{total}} ~~
a+{\overbrace{b+\cdots}}^{126}+z$