9.62.3 Can you answer these questions?

9.62.3.1 Foreach loop doesn't work inside mdframed to draw points

https://tex.stackexchange.com/landing/r/digest?cta=question&id=696261

In this case, I would like to plot some points from the graph of x^2 - x - 6 using foreach (coordinate in the MWE). Unfortunately, when I plug the foreach loop, the error stated 
Undefined control ... 
[tikz-pgf] [plot] [mdframed]
 

asked by Wilory Lu https://tex.stackexchange.com/landing/r/digest?cta=user&id=222046 Score of 1

9.62.3.2 3D Plot - Step Function

https://tex.stackexchange.com/landing/r/digest?cta=question&id=696527

I would like to generate a 3D picture for a step function, something like this: 
but I got stuck. Below, I tried something. 
\documentclass{article} 
\usepackage{tikz} 
\usetikzlibrary{3d} 
\begin{... 
[tikz-arrows] [tikz-styles] [3d] [tikz-3dplot] [tikz-3d]
 

asked by Iuli https://tex.stackexchange.com/landing/r/digest?cta=user&id=28568 Score of 1

9.62.3.3 Setting paper sizes with new commands

https://tex.stackexchange.com/landing/r/digest?cta=question&id=696375

I made a style file chil.sty residing in some library path with the following page sizes. 
\RequirePackage{geometry} 
\newcommand{\aluminpg} 
{\geometry{paperwidth=13cm,paperheight=21cm}} 
\newcommand{... 
[geometry]
 

asked by Prego https://tex.stackexchange.com/landing/r/digest?cta=user&id=304362 Score of 1