Function cases

pub fn cases<I>(items: I) -> MathML
where
    I: IntoIterator<Item = MathML>,

Renders a piecewise function.

Input

\begin{vmatrix} a & b \\ c & d \end{vmatrix}

Output

$$\Vert \begin{array}{cc}a& b\\ c& d\end{array}\Vert$$