# Case Condition for two lines

The main trick is using `aligned`

; however, there are other improvements to your code:

“div” is an operator and it's much better to define a macro for it; since

`\div`

is preempted, I used the name`\divop`

;if an operator immediately follows

`&`

in`align`

or`aligned`

, it should be preceded by`\!`

or a spurious thin space would be added; a little nuisance, but it's much better than`\mathrm{div}\,`

;`\boldsymbol`

works, but`\bm`

is better; remember to load`bm`

after`amsmath`

; you might keep`\boldsymbol`

, but`\bm`

is easier;`\bold`

is not predefined; probably you meant`\mathbf`

; I recommend using`\mathbf{u}`

and`\bm{\sigma}`

rather than`\mathbf u`

and`\bm \sigma`

: it's semantically sounder;`\overline`

is less appealing than`\bar`

for a single letter;`\tfrac`

is better in the context, because`\frac`

in`aligned`

would print a big fraction;`\left`

and`\right`

in that context are useless: they add unwanted space and produce oversized parentheses.

```
\documentclass{article}
\usepackage{amsmath,bm}
\DeclareMathOperator{\divop}{div}
\begin{document}
\begin{align*}
\begin{cases}
\begin{aligned}
&\bm{\varepsilon}(\mathbf{u}) = \tfrac{1}{2}(\nabla \mathbf{u} + \nabla \mathbf{u}^T ) \\
&\!\divop\bm{\sigma} + \mathbf{f} = \mathbf{0}
\end{aligned}&\text{in } \bm{\Omega}
\\
\mathbf{u} = \bar{\mathbf{u}} & \text{on } \partial \bm{\Omega}_D \\
\bm{\sigma} \mathbf{n} = \bar{\mathbf{t}} & \text{on } \partial \bm{\Omega}_N
\end{cases}
\end{align*}
\end{document}
```

Like this? B.t.w., `\bold`

is not defined. I replaced it with `\bm`

.

```
\documentclass{article}
\usepackage[utf8]{inputenc}%
\usepackage{mathtools, bm}
\newcommand{\Leg}[3][]{\left(\frac{#2}{#3}\right)_{#1}}
\DeclareMathOperator{\divg}{div}
\begin{document}
\begin{align*}
\begin{cases}
\boldsymbol\varepsilon(\bm{u}) = \frac{1}{2}\left(\nabla \bm{u} + \nabla \bm{u}^T \right) & \smash{\raisebox{-1.6ex}{in $\boldsymbol\Omega$}} \\
\divg\boldsymbol \sigma + \bm{f} = \mathbf{0} \\
\bm{u} = \overline{\bm{u}} & \text{on } \partial \boldsymbol\Omega_D \\
\boldsymbol \sigma \bm{n}= \overline{\bm{t}} & \text{on } \partial \boldsymbol\Omega_N
\end{cases}
\end{align*}
\[ \Leg{\pi}{θ}\quad \Leg{\pi}{θ} \]%
\end{document}
```