(一)數(shù)學符號列表
希臘字母
Symbol |
Script |
Symbol |
Script |
and
|
A and \alpha |
and
|
N and \nu |
and
|
B and \beta |
and
|
\Xi and \xi |
and
|
\Gamma and \gamma |
and
|
O and o |
and
|
\Delta and \delta |
, and
|
\Pi, \pi and \varpi |
, and
|
E, \epsilon and \varepsilon |
, and
|
P, \rho and \varrho |
and
|
Z and \zeta |
, and
|
\Sigma, \sigma and \varsigma |
and
|
H and \eta |
and
|
T and \tau |
, and
|
\Theta, \theta and \vartheta |
and
|
\Upsilon and \upsilon |
and
|
I and \iota |
, and
|
\Phi, \phi and \varphi |
, and
|
K, \kappa and \varkappa |
and
|
X and \chi |
and
|
\Lambda and \lambda |
and
|
\Psi and \psi |
and
|
M and \mu |
and
|
\Omega and \omega |
三角函數(shù)
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
 |
\sin |
|
 |
\arcsin |
|
 |
\sinh |
|
 |
\sec |
 |
\cos |
|
 |
\arccos |
|
 |
\cosh |
|
 |
\csc |
 |
\tan |
|
 |
\arctan |
|
 |
\tanh |
|
|
|
 |
\cot |
|
|
|
|
 |
\coth |
|
|
|
關(guān)系符號
Symbol |
Script |
|
Symbol |
Script |
 |
< |
|
 |
> |
 |
\leq |
|
 |
\geq |
 |
\ll |
|
 |
\gg |
 |
\subset |
|
 |
\supset |
 |
\subseteq |
|
 |
\supseteq |
 |
\nsubseteq |
|
 |
\nsupseteq |
 |
\sqsubset |
|
 |
\sqsupset |
 |
\sqsubseteq |
|
 |
\sqsubseteq |
 |
\preceq |
|
 |
\succeq |
 |
\because |
|
 |
\therefore |
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
 |
= |
|
 |
\parallel |
|
 |
\nparallel |
 |
\doteq |
|
 |
\asymp |
|
 |
\bowtie |
 |
\equiv |
|
 |
\vdash |
|
 |
\dashv |
 |
\approx |
|
 |
\in |
|
 |
\ni |
 |
\cong |
|
 |
\smile |
|
 |
\frown |
 |
\simeq |
|
 |
\models |
|
 |
\notin |
 |
\sim |
|
 |
\perp |
|
 |
\mid |
 |
\propto |
|
 |
\prec |
|
 |
\succ |
 |
\neq |
|
 |
\sphericalangle |
|
 |
\measuredangle |
二元運算
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
 |
\pm |
|
 |
\cap |
|
 |
\diamond |
|
 |
\oplus |
 |
\mp |
|
 |
\cup |
|
 |
\bigtriangleup |
|
 |
\ominus |
 |
\times |
|
 |
\uplus |
|
 |
\bigtriangledown |
|
 |
\otimes |
 |
\div |
|
 |
\sqcap |
|
 |
\triangleleft |
|
 |
\oslash |
 |
\ast |
|
 |
\sqcup |
|
 |
\triangleright |
|
 |
\odot |
 |
\star |
|
 |
\vee |
|
 |
\bigcirc |
|
 |
\circ |
 |
\dagger |
|
 |
\wedge |
|
 |
\bullet |
|
 |
\setminus |
 |
\ddager |
|
 |
\cdot |
|
 |
\wr |
|
 |
\amalg |
集合邏輯
Symbol |
Script |
|
Symbol |
Script |
 |
\exists |
|
 |
\rightarrow |
 |
\nexists |
|
 |
\leftarrow |
 |
\forall |
|
 |
\mapsto |
 |
\neg |
|
 |
\implies |
 |
\subset |
|
 |
\Rightarrow |
 |
\supset |
|
 |
\leftrightarrow |
 |
\in |
|
 |
\iff |
 |
\notin |
|
 |
\Leftrightarrow |
 |
\ni |
|
 |
\top |
 |
\land |
|
 |
\bot |
 |
\lor |
|
and
|
\emptyset and \varnothing |
 |
\angle |
|
 |
\rightleftharpoons |
界限
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
 |
\mid |
|
|
|
|
 |
/ |
|
 |
\backslash |
 |
{ |
|
 |
} |
|
 |
\langle |
|
 |
\rangle |
 |
\uparrow |
|
 |
\Uparrow |
|
 |
\lceil |
|
 |
\rceil |
 |
\downarrow |
|
 |
\Downarrow |
|
 |
\lfloor |
|
 |
\rfloor |
其他
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
 |
\partial |
|
 |
\imath |
|
 |
\Re |
|
 |
\nabla |
|
 |
\aleph |
 |
\eth |
|
 |
\jmath |
|
 |
\Im |
|
 |
\Box |
|
 |
\beth |
 |
\hbar |
|
 |
\ell |
|
 |
\wp |
|
 |
\infty |
|
 |
\gimel |
求和積分
Symbol |
Script |
|
Symbol |
Script |
|
Symbol |
Script |
 |
\sum |
|
 |
\prod |
|
 |
\coprod |
 |
\bigoplus |
|
 |
\bigotimes |
|
 |
\bigodot |
 |
\bigcup |
|
 |
\bigcap |
|
 |
\biguplus |
 |
\bigsqcup |
|
 |
\bigvee |
|
 |
\bigwedge |
 |
\int |
|
 |
\oint |
|
 |
\iint |
 |
\iiint |
|
 |
\iiiint |
|
 |
\idotsint |
自定義操作符
$\operatorname{arg\,max}_a f(a) = \operatorname*{arg\,max}_b f(b)$
$\DeclareMathOperator*{\argmax}{arg\,max}
\argmax_c f(c)$
%20%3D%20%5Coperatorname*%7Barg%5C%2Cmax%7D_b%20f(b))
)
(二)上下標
上標^
下標_
- 例子一
k_{n+1} = n^2 + k_n^2 - k_{n-1}
- 例子二
n^{22}
- 例子三
f(n) = n^5 + 4n^2 + 2 |_{n=17}
(三)分數(shù)與二項式
分數(shù)\frac{numerator}{denominator}
二項式\binom{numerator}{numerator}
- 例子一
\frac{n!}{k!(n-k)!} = \binom{n}{k}
- 例子二
\frac{\frac{1}{x}+\frac{1}{y}}{y-z}
- 例子三
^3/_7
- 連分數(shù)
\begin{equation}
x = a_0 + \cfrac{1}{a_1
+ \cfrac{1}{a_2
+ \cfrac{1}{a_3 + \cfrac{1}{a_4} } } }
\end{equation}

\begin{equation}
\frac{
\begin{array}[b]{r}
\left( x_1 x_2 \right)\\
\times \left( x'_1 x'_2 \right)
\end{array}
}{
\left( y_1y_2y_3y_4 \right)
}
\end{equation}
![\begin{equation} \frac{ \begin{array}[b]{r} \left( x_1 x_2 \right)\\ \times \left( x'_1 x'_2 \right) \end{array} }{ \left( y_1y_2y_3y_4 \right) } \end{equation}](https://math.jianshu.com/math?formula=%5Cbegin%7Bequation%7D%20%5Cfrac%7B%20%5Cbegin%7Barray%7D%5Bb%5D%7Br%7D%20%5Cleft(%20x_1%20x_2%20%5Cright)%5C%5C%20%5Ctimes%20%5Cleft(%20x'_1%20x'_2%20%5Cright)%20%5Cend%7Barray%7D%20%7D%7B%20%5Cleft(%20y_1y_2y_3y_4%20%5Cright)%20%7D%20%5Cend%7Bequation%7D)
(四)根
根\sqrt
- 例子一
\sqrt{\frac{a}侈离}
- 例子二
\sqrt[n]{1+x+x^2+x^3+\dots+x^n}
(五)求和積分
求和\sum
積分\int
- 例子一
\sum_{i=1}^{10} t_i
- 例子二
\int_0^\infty \mathrm{e}^{-x}\,\mathrmmggcnlcx
-
\substack
用法
\sum_{\substack{
0<i<m \\
0<j<n
}}
P(i,j)
)
- 改變位置
\int\limits_a^b
(六)括號分割符
![( a ), [ b ], \{ c \}, | d |, \ |e\ |, \langle f \rangle, \lfloor g \rfloor, \lceil h \rceil, \ulcorner i \urcorner](https://math.jianshu.com/math?formula=(%20a%20)%2C%20%5B%20b%20%5D%2C%20%5C%7B%20c%20%5C%7D%2C%20%7C%20d%20%7C%2C%20%5C%20%7Ce%5C%20%7C%2C%20%5Clangle%20f%20%5Crangle%2C%20%5Clfloor%20g%20%5Crfloor%2C%20%5Clceil%20h%20%5Crceil%2C%20%5Culcorner%20i%20%5Curcorner)
- 自動調(diào)整大小
\left
隧饼,\right
巡李,\middle
斟或。
\left(\frac{x^2}{y^3}\right)
)
P\left(A=2\middle|\frac{A^2}{B}>4\right)
)
\left\{\frac{x^2}{y^3}\right\}

\left.\frac{x^3}{3}\right|_0^1
- 手動調(diào)整大小
( \big( \Big( \bigg( \Bigg(

\frac{\mathrm d}{\mathrm d x} \left( k g(x) \right)
%20%5Cright))
\frac{\mathrm d}{\mathrm d x} \big( k g(x) \big)
(七)矩陣
\begin{matrix}
a & b & c \\
d & e & f \\
g & h & i
\end{matrix}

名稱 |
分隔符 |
pmatrix |
( ) |
pmatrix* |
( ) |
bmatrix |
[ ] |
bmatrix* |
[ ] |
Bmatrix |
{ } |
Bmatrix* |
{ } |
vmatrix |
| | |
vmatrix* |
| | |
Vmatrix |
|| || |
Vmatrix* |
|| || |
A_{m,n} =
\begin{pmatrix}
a_{1,1} & a_{1,2} & \cdots & a_{1,n} \\
a_{2,1} & a_{2,2} & \cdots & a_{2,n} \\
\vdots & \vdots & \ddots & \vdots \\
a_{m,1} & a_{m,2} & \cdots & a_{m,n}
\end{pmatrix}

\begin{array}{c|c}
1 & 2 \\
\hline
3 & 4
\end{array}

M = \begin{bmatrix}
\frac{5}{6} & \frac{1}{6} & 0 \\[0.3em]
\frac{5}{6} & 0 & \frac{1}{6} \\[0.3em]
0 & \frac{5}{6} & \frac{1}{6}
\end{bmatrix}
![M = \begin{bmatrix} \frac{5}{6} & \frac{1}{6} & 0 \\[0.3em] \frac{5}{6} & 0 & \frac{1}{6} \\[0.3em] 0 & \frac{5}{6} & \frac{1}{6} \end{bmatrix}](https://math.jianshu.com/math?formula=M%20%3D%20%5Cbegin%7Bbmatrix%7D%20%5Cfrac%7B5%7D%7B6%7D%20%26%20%5Cfrac%7B1%7D%7B6%7D%20%26%200%20%5C%5C%5B0.3em%5D%20%5Cfrac%7B5%7D%7B6%7D%20%26%200%20%26%20%5Cfrac%7B1%7D%7B6%7D%20%5C%5C%5B0.3em%5D%200%20%26%20%5Cfrac%7B5%7D%7B6%7D%20%26%20%5Cfrac%7B1%7D%7B6%7D%20%5Cend%7Bbmatrix%7D)
A matrix in text must be set smaller:
$\bigl(\begin{smallmatrix}
a&b \\ c&d
\end{smallmatrix} \bigr)$
to not increase leading in a portion of text.
A matrix in text must be set smaller:
)
to not increase leading in a portion of text.
(八)文本格式
- 文本
- 字體
公式 |
例子 |
\mathrm{…} |
 |
\mathit{…} |
 |
\mathbf{…} |
 |
\mathsf{…} |
 |
\mathtt{…} |
 |
\mathfrak{…} |
 |
\mathcal{…} |
 |
\mathbb{…} |
 |
\mathscr{…} |
 |
- 例子
- 強調(diào)
公式 |
例子 |
|
公式 |
例子 |
 |
a' |
|
 |
a'' |
 |
\hat{a} |
|
 |
\bar{a} |
 |
\grave{a} |
|
 |
\acute{a} |
 |
\dot{a} |
|
 |
\ddot{a} |
 |
\not{a} |
|
 |
\mathring{a} |
 |
\overrightarrow{a} |
|
 |
\overleftarrow{a} |
 |
a''' |
|
 |
a'''' |
 |
\overline{aaa} |
|
 |
\check{a} |
 |
\breve{a} |
|
 |
\vec{a} |
 |
\dddot{a} |
|
 |
\ddddot{a} |
 |
\widehat{AAA} |
|
 |
\widetilde{AAA} |
 |
\stackrel\frown{AAA} |
|
|
|
 |
\tilde{a} |
|
 |
\underline{a} |
(九)顏色
k = {\color{red}x} \mathbin{\color{blue}-} 2

顏色 |
代碼 |
 |
\color{black}{text} |
 |
\color{gray}{text} |
 |
\color{silver}{text} |
 |
\color{white}{text} |
 |
\color{maroon}{text} |
 |
\color{red}{text} |
 |
\color{yellow}{text} |
 |
\color{lime}{text} |
 |
\color{olive}{text} |
 |
\color{green}{text} |
 |
\color{teal}{text} |
 |
\color{aqua}{text} |
 |
\color{blue}{text} |
 |
\color{navy}{text} |
 |
\color{purple}{text} |
 |
\color{fuchsia}{text} |
(十)控制
f(n) =
\begin{cases}
n/2 & \quad \text{if } n \text{ is even}\\
-(n+1)/2 & \quad \text{if } n \text{ is odd}
\end{cases}
%20%3D%20%5Cbegin%7Bcases%7D%20n%2F2%20%26%20%5Cquad%20%5Ctext%7Bif%20%7D%20n%20%5Ctext%7B%20is%20even%7D%5C%5C%20-(n%2B1)%2F2%20%26%20%5Cquad%20%5Ctext%7Bif%20%7D%20n%20%5Ctext%7B%20is%20odd%7D%20%5Cend%7Bcases%7D)
公式 |
大小 |
\, |
3/18 of a quad |
\: |
4/18 of a quad |
\; |
5/18 of a quad |
\! |
-3/18 of a quad |
\quad |
a quad |
\qquad |
2 quad |
\int y\, \mathrmr2dnc2kx

\int y\: \mathrmbt3jurjx

\int y\; \mathrmy8itacpx

\left(
\begin{array}{c}
n \\
r
\end{array}
\right) = \frac{n!}{r!(n-r)!}
%20%3D%20%5Cfrac%7Bn!%7D%7Br!(n-r)!%7D)
\left(\!
\begin{array}{c}
n \\
r
\end{array}
\!\right) = \frac{n!}{r!(n-r)!}
%20%3D%20%5Cfrac%7Bn!%7D%7Br!(n-r)!%7D)
- 定義新命令
- 例子
\begin{equation}
C^i_j = {\textstyle \sum_k} A^i_k B^k_j
\end{equation}

例子 |
公式 |
 |
\dots |
 |
\ldots |
 |
\cdots |
 |
\vdots |
 |
\ddots |
$A_1,A_2,\dotsc,$
$A_1+\dotsb+A_N$
$A_1 \dotsm A_N$
$\int_a^b \dotsi$
$A_1\dotso A_N$





(十一)特殊用法
- 其他位置標記
\overset
,\underset
。
A \overset{!}{=} B; A \stackrel{!}{=} B

\lim_{x\to 0}{\frac{e^x-1}{2x}}
\overset{\left[\frac{0}{0}\right]}{\underset{\mathrm{H}}{=}}
\lim_{x\to 0}{\frac{e^x}{2}}={\frac{1}{2}}
![\lim_{x\to 0}{\frac{e^x-1}{2x}} \overset{\left[\frac{0}{0}\right]}{\underset{\mathrm{H}}{=}} \lim_{x\to 0}{\frac{e^x}{2}}={\frac{1}{2}}](https://math.jianshu.com/math?formula=%5Clim_%7Bx%5Cto%200%7D%7B%5Cfrac%7Be%5Ex-1%7D%7B2x%7D%7D%20%5Coverset%7B%5Cleft%5B%5Cfrac%7B0%7D%7B0%7D%5Cright%5D%7D%7B%5Cunderset%7B%5Cmathrm%7BH%7D%7D%7B%3D%7D%7D%20%5Clim_%7Bx%5Cto%200%7D%7B%5Cfrac%7Be%5Ex%7D%7B2%7D%7D%3D%7B%5Cfrac%7B1%7D%7B2%7D%7D)
\overbrace
辛辨,\underbrace
十气。
z = \overbrace{
\underbrace{x}_\text{real} + i
\underbrace{y}_\text{imaginary}
}^\text{complex number}

y = a + f(\underbrace{b x}_{
\ge 0 \text{ by assumption}})
)
A \xleftarrow{\text{this way}} B
\xrightarrow[\text{or that way}]{ } C
![A \xleftarrow{\text{this way}} B \xrightarrow[\text{or that way}]{ } C](https://math.jianshu.com/math?formula=A%20%5Cxleftarrow%7B%5Ctext%7Bthis%20way%7D%7D%20B%20%5Cxrightarrow%5B%5Ctext%7Bor%20that%20way%7D%5D%7B%20%7D%20C)
$\begin{align*}
f(x) &= a x^2+b x +c & g(x) &= d x^3 \\
f'(x) &= 2 a x +b & g'(x) &= 3 d x^2
\end{align*}$
%20%26%3D%20a%20x%5E2%2Bb%20x%20%2Bc%20%26%20g(x)%20%26%3D%20d%20x%5E3%20%5C%5C%20f'(x)%20%26%3D%202%20a%20x%20%2Bb%20%26%20g'(x)%20%26%3D%203%20d%20x%5E2%20%5Cend%7Balign*%7D)
f(x) = \left\{
\begin{array}{lr}
x^2 & : x < 0\\
x^3 & : x \ge 0
\end{array}
\right.
%20%3D%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Blr%7D%20x%5E2%20%26%20%3A%20x%20%3C%200%5C%5C%20x%5E3%20%26%20%3A%20x%20%5Cge%200%20%5Cend%7Barray%7D%20%5Cright.)
u(x) =
\begin{cases}
\exp{x} & \text{if } x \geq 0 \\
1 & \text{if } x < 0
\end{cases}
%20%3D%20%5Cbegin%7Bcases%7D%20%5Cexp%7Bx%7D%20%26%20%5Ctext%7Bif%20%7D%20x%20%5Cgeq%200%20%5C%5C%201%20%26%20%5Ctext%7Bif%20%7D%20x%20%3C%200%20%5Cend%7Bcases%7D)
\begin{equation}
\left.\begin{aligned}
B'&=-\partial \times E,\\
E'&=\partial \times B - 4\pi j,
\end{aligned}
\right\}
\qquad \text{Maxwell's equations}
\end{equation}

\begin{alignat}{2}
\sigma_1 &= x + y &\quad \sigma_2 &= \frac{x}{y} \\
\sigma_1' &= \frac{\partial x + y}{\partial x} & \sigma_2'
&= \frac{\partial \frac{x}{y}}{\partial x}
\end{alignat}

\begin{gather*}
a_0=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}f(x)\,\mathrma2krrmkx\\[6pt]
\begin{split}
a_n=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}f(x)\cos nx\,\mathrmapalhu7x=\\
=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}x^2\cos nx\,\mathrm2yfqeg3x
\end{split}\\[6pt]
\begin{split}
b_n=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}f(x)\sin nx\,\mathrma7vozbgx=\\
=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}x^2\sin nx\,\mathrm787al22x
\end{split}\\[6pt]
\end{gather*}
![\begin{gather*} a_0=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}f(x)\,\mathrmdzyfrpcx\\[6pt] \begin{split} a_n=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}f(x)\cos nx\,\mathrmkfbnj72x=\\ =\frac{1}{\pi}\int\limits_{-\pi}^{\pi}x^2\cos nx\,\mathrmzoookbkx \end{split}\\[6pt] \begin{split} b_n=\frac{1}{\pi}\int\limits_{-\pi}^{\pi}f(x)\sin nx\,\mathrmonzfbinx=\\ =\frac{1}{\pi}\int\limits_{-\pi}^{\pi}x^2\sin nx\,\mathrmawaww7ox \end{split}\\[6pt] \end{gather*}](https://math.jianshu.com/math?formula=%5Cbegin%7Bgather*%7D%20a_0%3D%5Cfrac%7B1%7D%7B%5Cpi%7D%5Cint%5Climits_%7B-%5Cpi%7D%5E%7B%5Cpi%7Df(x)%5C%2C%5Cmathrm%7Bd%7Dx%5C%5C%5B6pt%5D%20%5Cbegin%7Bsplit%7D%20a_n%3D%5Cfrac%7B1%7D%7B%5Cpi%7D%5Cint%5Climits_%7B-%5Cpi%7D%5E%7B%5Cpi%7Df(x)%5Ccos%20nx%5C%2C%5Cmathrm%7Bd%7Dx%3D%5C%5C%20%3D%5Cfrac%7B1%7D%7B%5Cpi%7D%5Cint%5Climits_%7B-%5Cpi%7D%5E%7B%5Cpi%7Dx%5E2%5Ccos%20nx%5C%2C%5Cmathrm%7Bd%7Dx%20%5Cend%7Bsplit%7D%5C%5C%5B6pt%5D%20%5Cbegin%7Bsplit%7D%20b_n%3D%5Cfrac%7B1%7D%7B%5Cpi%7D%5Cint%5Climits_%7B-%5Cpi%7D%5E%7B%5Cpi%7Df(x)%5Csin%20nx%5C%2C%5Cmathrm%7Bd%7Dx%3D%5C%5C%20%3D%5Cfrac%7B1%7D%7B%5Cpi%7D%5Cint%5Climits_%7B-%5Cpi%7D%5E%7B%5Cpi%7Dx%5E2%5Csin%20nx%5C%2C%5Cmathrm%7Bd%7Dx%20%5Cend%7Bsplit%7D%5C%5C%5B6pt%5D%20%5Cend%7Bgather*%7D)
begin{equation}
\boxed{x^2+y^2 = z^2}
\end{equation}

\begin{equation}
\lim_{a\to \infty} \tfrac{1}{a}
\end{equation}

\begin{equation}
\lim\nolimits_{a\to \infty} \tfrac{1}{a}
\end{equation}

\begin{equation}
\int_a^b x^2 \mathrm3vrrr37 x
\end{equation}

\begin{equation}
\int\limits_a^b x^2 \mathrm3hhlhuo x
\end{equation}

\begin{equation}
\lim_{a \underset{>}{\to} 0} \frac{1}{a}
\end{equation}

\begin{equation}
\sum\nolimits' C_n
\end{equation}

\begin{equation}
\sum_{n=1}\nolimits' C_n
\end{equation}

\begin{equation}
\sideset{}{'}\sum_{n=1}C_n
\end{equation}

\begin{equation}
\sideset{_a^b}{_c^d}\sum
\end{equation}

\begin{equation}
{\sum\limits_{n=1} }'C_n
\end{equation}

命令 |
例子 |
\displaystyle {ABCDabcd1234} |
 |
\textstyle{ABCDabcd1234} |
 |
\scriptstyle{ABCDabcd1234} |
 |
\scriptscriptstyle{ABCDabcd1234} |
 |
\begin{equation}
x = a_0 + \frac{1}{a_1 + \frac{1}{a_2 + \frac{1}{a_3 + a_4}}}
\end{equation}

\begin{equation}
x = a_0 + \frac{1}{\displaystyle a_1
+ \frac{1}{\displaystyle a_2
+ \frac{1}{\displaystyle a_3 + a_4}}}
\end{equation}

$a \equiv b \pmod n$
