9.18.3 Can you answer these questions?

9.18.3.1 Issues with vertical spacing and \addcontentsline

https://tex.stackexchange.com/landing/r/digest?cta=question&id=679825

The code \vskip\baselineskip\addvspace{0.5\baselineskip} produces a vertical space equal to \baselineskip, as it should. 
However, when I add \addcontentsline in the middle, I get a bigger space: 
\... 
[spacing] [tex-core] [vertical-spacing]
 

asked by Michael Fraiman https://tex.stackexchange.com/landing/r/digest?cta=user&id=100689 Score of 1

9.18.3.2 How can I use conflicting libraries in latex?

https://tex.stackexchange.com/landing/r/digest?cta=question&id=679833

I am trying to write a document that uses two other manuscripts which make use of different libraries that seem to overlap in functionality. 
Specifically when I try to use 
\usepackage[linesnumbered, ... 
[math-mode] [algorithms]
 

asked by Alex https://tex.stackexchange.com/landing/r/digest?cta=user&id=282350 Score of 1

9.18.3.3 How can I list code with alignment and syntax highlighting?

https://tex.stackexchange.com/landing/r/digest?cta=question&id=679612

I would like to effectively typeset code in a proportional font with syntax highlighting and horizontal alignment. How can I do that? 
The package listings offers syntax highlighting but not alignment. ... 
[horizontal-alignment] [listings] [code] [tabbing]
 

asked by matj1 https://tex.stackexchange.com/landing/r/digest?cta=user&id=161116 Score of 1