7.17.3 Can you answer these questions?

7.17.3.1 Installing nicematrix in texmaker macOS

https://tex.stackexchange.com/landing/r/digest?cta=question&id=586171

I asked a question today in Trying to personalize this code for block matrices 
, where the suggestion was to use the nicematrix package. 
The readme file inhttps://www.ctan.org/pkg/nicematrix suggests ... 
[texmaker] [texmf] [nicematrix]
 

asked by Ofelia y Orquesta https://tex.stackexchange.com/landing/r/digest?cta=user&id=236872 1 vote

7.17.3.2 Rightmark of \subsection disappear when it's on the same page with \section

https://tex.stackexchange.com/landing/r/digest?cta=question&id=586066

In a two-sided article, I wish to show the current subsection name on the odd pages, and the current section name on even pages. Therefore I wrote 
\fancyhead[RO]{\rightmark} 
\fancyhead[LE]{\leftmark} 
\... 
[fancyhdr]
                                                                                  

                                                                                  
 

asked by Jinwen https://tex.stackexchange.com/landing/r/digest?cta=user&id=194994 1 vote

7.17.3.3 ChkTeX fails with nested math mode

https://tex.stackexchange.com/landing/r/digest?cta=question&id=586193

MWE: 
\begin{align} 
\begin{array} {l} 
abc 
\end{array} \\ 
3 - 2 = 1 
\pi 
\end{align} 
ChkTeX detects "Wrong length of dash" in 3 - 2 = 1 and "Command terminated ... 
[math-mode] [chktex]
 

asked by DKozl https://tex.stackexchange.com/landing/r/digest?cta=user&id=231894 1 vote