9.39.3 Can you answer these questions?

9.39.3.1 Make a tag in a command from given arguments

https://tex.stackexchange.com/landing/r/digest?cta=question&id=688225

I am trying to make a LaTeX document for maths notes. 
I have written the following commands: 
\newcommand{\definition}[2]{\textbf{Definition} (#1): #2 \index{#1} \tag{definition_#1}} 
\newcommand{\... 
[tags]
 

asked by Robin https://tex.stackexchange.com/landing/r/digest?cta=user&id=220881 Score of 1

9.39.3.2 Incorrect Display of Plotting

https://tex.stackexchange.com/landing/r/digest?cta=question&id=688091

I am graphing a function and I would like to label two points on the axis. One point is labeled correctly, but the other point is displaying the number 4 instead of the corresponding letter. How can I ... 
[tikz-pgf] [pgfplots]
 

asked by Santiago Sierra https://tex.stackexchange.com/landing/r/digest?cta=user&id=262545 Score of 1

9.39.3.3 BibTex not citing one particular entry in et al. format

https://tex.stackexchange.com/landing/r/digest?cta=question&id=688240

The entry in the bib file is: 
@article{singhsetal2003, 
title={On the use of modified randomization device for estimating the prevalence of a sensitive attribute}, 
author={Singh, S and Horn, S and ... 
[bibliographies] [citing] [harvard-style]
 

asked by Diya https://tex.stackexchange.com/landing/r/digest?cta=user&id=267015 Score of 1

answered by Mico https://tex.stackexchange.com/landing/r/digest?cta=user&id=5001 Score of 0