Adding letters to theorem labels to specify the theorem is in the appendix with package amsthm

Question

So I have a main document with a couple of theorems in it. I also have an appendix with theorems that might be less important to most readers. These are two separate documents. Ideally, the answer won't use a bunch of extra packages [preferably just 'amsthm']. Unfortunately, my collaborators used word for the main document since the content was mostly much less mathematical. Anyways, in the appendix, I'd like something like

Theorem S1. < insert text >

Theorem S2. < insert text >

Corralary S1. < insert text >

The S stands for the supplement (could also use A for appendix). This means I can refer to theorems in the main document, and it is clear it is not referring to the two main mathematical results presented there.

I did see one question about adding letters to subsections, but when I tried adapting the code to the theorem environment it didn't work.

Answer 1

One option is to do as follows, using

\usepackage{amsthm}
\newtheorem{thm}{Theorem S\ignorespaces}
\begin{document}
\begin{thm}
This is a theorem with S in it.
\end{thm}
\end{document}

Answer 2

You could do something like this (untested—my laptop is in for repairs so I don't have a LaTeX install handy):

\newtheorem{thm}{Theorem}
\renewcommand{\thethm}{S\arabic{thm}}