AMS – Definitions, Theorems, Lemmas and more

AMS-flavored LaTeX introduces a flexible language for declaring custom types of environments. It has long been the weapon of choice for declaring mathematical statements, for example:

  % Declare in header.tex:
  \newtheorem{theorem}{Theorem}
  \newtheorem{proof}{Proof}
  % 
  % And later use:
  \begin{theorem}[Pythagoras]
    Suppose $a\leq b\leq c$ are the side-lengths of a right triangle.\\
    Then $a^2+b^2=c^2$.
  \end{theorem}
  \begin{proof}
    Proof is left as an exercise to the reader.
  \end{proof}

Suppose \(a\leq b\leq c\) are the side-lengths of a right triangle.
Then \(a^{2}+b^{2}=c^{2}\).

Proof is left as an exercise to the reader.