Using braket package with Lyx with WYSIWYG

Question

The braket package defines Dirac's braket notation. To use it in Lyx, I add the line:

\usepackage{braket}

to the LaTeX preamble. Then Lyx will be able to compile commands like \bra and \ket. Problem is that the Lyx editor itself won't recognize this commands.

If instead of using the braket package I had defined math-macros for the commands \bra, \ket, etc., I could tell Lyx how these things should look in the editor. That is, I can tell it to put an \rangle before the argument (that Lyx knows how to draw) and a | after.

Is there a way to use the \bra, \ket, etc., commands from the braket package, and still be able to tell Lyx how these should look in the editor?

EDIT: Right after posting, I discovered this question, which mentions the Instant Preview feature of Lyx. Although this kind of fixes my issue, it's not exactly what I want. I want to be able to specify what the command should look like in the editor, in terms of other commands that Lyx already recognizes (in the editor), like I would do with a math-macro.

Answer 1

Place \let\realket\ket in your preamble, and then redefine \ket using LyX's new command feature, providing LyX with the TeX code to use and the LyX code to display.

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\let, like \def, takes two arguments. When you say \let\realket\ket, you instruct TeX to copy the definition of \ket into \realket. This differs from \def in as much as \ket isn't itself mentioned in the definition of \realket (IIRC, it's a one-level-deep copy), whereas \def\realket\ket would simply have \realket 'pointing to' \ket, where \kets definition could change at any time. Since the definition of \ket from braket is saved into \realket, you are free to redefine \ket to whatever you please :)

Answer 2

This inconvenience is finally solved in From LyX-2.4.0-beta3 (format 616). You can just fill the LyX box to define how the macro displays in LyX and leave the TeX box empty, and things will work as expected.

As written in the LyX source code:

* Format incremented to 616: Do not output LaTeX for a macro if the LaTeX part is empty
- This allows the user to define the LyX display for LaTeX commands
  that are already defined (e.g., in user preamble or a package).