# Error with begin{Proof}…\end{Proof} command

I have written the following code:

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\newtheorem{theorem}{Theorem}
\newtheorem{lemma}{Lemma}

\begin{document}

\begin{lemma}
My lemma
\end{lemma}

\begin{Proof}
My proof
\end{Proof}

\end{document}


It shows the following error

! LaTeX Error: Environment Proof undefined.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.15 \begin{Proof}
Type I <command> <return> to replace it with another command,
or <return> to continue without it.
! LaTeX Error: \begin{document} ended by \end{Proof}.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.17 \end{Proof}
Type I <command> <return> to replace it with another command,
or <return> to continue without it.


• Welcome! It should be \begin{proof} and \end{proof}. LaTeX commands are case sensitive. – egreg Dec 20 '16 at 10:39
Case sensitivity is the problem: Proof should be proof. Please try with
\begin{proof}