JH tries

getting amsthm to work in the template

(the standard approach will not work because of conflicts with cleveref)

That's why

1. if amsthm is loaded in the main document's preamble
2. the newtheorem statements have to either

• be called after begin{document} or
• wrapped in \AtBeginDocument{}

This merge requests includes

1. \usepackage{amsthm}
2. \newtheorem Theorem/Lemma with \AtBeginDocument
3. documentation and examples as Section 4.2. Math Environments