自用的markdown与latex特殊符号

有些特殊符号不经常用老是忘，偶尔用的时候还得查，总结一下备用。

\triangleq
\approx
\xlongequal[y=\arctan x]{x=\tan y}
\sum_{\substack{j=1 \\ j\neq i}}
\iiint\limits_\Omega
\overset{\circ}{\vec{r}}
\varphi
\checkmark
\stackrel{\cdot\cdot\cdot}{x}
\equiv

$$\triangleq \approx \xlongequal[y=\arctan x]{x=\tan y} \sum_{\substack{j=1 \\ j\neq i}} \iiint\limits_\Omega \overset{\circ}{\vec{r}} \varphi \checkmark \stackrel{\cdot\cdot\cdot}{x} \geqslant \equiv$$

$\LaTeX$ Mathematical Symbols
List of LaTeX mathematical symbols -oeis
List of Greek letters and math symbols -overleaf