SOLVED add appendix to a chapter

[Wolfgang Engelmann]

Thanks to all who helped me with the appendix to a chapter.
The following link
https://github.com/scottkosty/lyx-princeton-diss
allows to download the scottkosty /lyx-princeton-diss
(use the green box "code")
The trick is to put (by using the \usepackage{appendix} in the preamble 
behind the place where one wants to insert the subappendix/ces (here 
chapter 3) the following (as an example):

\begin{subappendices}

Appendix

3.4.1 First appendix of Chapter 3

3.4.2 Second appendix of Chapter 3

\end{subappendices}

I modified it to get the appendix in a section, not chapter by changing 
the nesting depth of the item and changed to appendix of section 3

   Works nicely.

Wolfgang