I need to do two vertical lines in LyX like this:

Two vertical lines

How to do that?

  • According to the LyX wiki it is Ctrl+Return. Jul 22, 2016 at 8:23
  • This shortcut produce me only a line break. Jul 22, 2016 at 9:31
  • I only know how to write it in LaTeX: \left\| \begin{array}{l} \textit{For~} a \\ f(a') \\ \end{array} \right. Jul 22, 2016 at 9:59
  • Or in text-mode \begin{tabular}{||l} \textit{For} $a$ \\ $f(a')$ \\ \end{tabular} Jul 22, 2016 at 10:01

2 Answers 2


To have an equivalent of the LaTeX \left\| \begin{array}{l} \mbox{For } a \\ f(a') \\ \end{array} \right.

First, you go I̲nsert>Math̲>Delimiter̲s

You uncheck the box "Keep matched" and you chose the correct left and right: Delimiters

Then, inside these delimiters, you will be in maths mode and have access to the maths toolbar. Add a matrix 2x1: enter image description here

Finally, you may want to use a \mbox for your "For ", Lyx should auto-complete.

Fill the matrix with the wanted elements, and you get:


You could also use \textit instead of the \mbox and have:



You could use some ERT (type <CTRL+l> for that, thats 'l' like in latex) and insert \vline{}~\vline{} into its box (thats LaTeX code for 'vertical line', 'space', 'vertical line').
Move out of the ERT box and write your math to the right of it.

The lines on the left will be the same height as your math on the right of it.

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