Proof without numbering

I am trying to remove the number from proof, but I could not. When I used amsthm package I got several errors. How to remove numbering of proofs without using amsthm package?

\documentclass[11pt]{article} \usepackage{mathtools}\mathtoolsset{showonlyrefs}                         \usepackage{amsfonts,amssymb,amsmath,microtype}\usepackage{enumitem}\usepackage{graphicx}\graphicspath{ {./images/} }\usepackage{algorithmicx}\usepackage{algorithm}\usepackage{algpseudocode}\def\NoNumber#1{{\def\alglinenumber##1{}\State #1}\addtocounter{ALG@line}{-1}}%\usepackage{mymacro}\usepackage[usenames,dvipsnames]{color}\usepackage{epsfig}\newtheorem{definition}{Definition}\newtheorem{thm}{Theorem}\newtheorem{prop}[thm]{Proposition}\newtheorem{lem}[thm]{Lemma}\newtheorem{Corollary}[thm]{Corollary}\newtheorem{pro}[thm]{Proof}\newtheorem{example}{Example}[section]\setcounter{secnumdepth}{3}\setcounter{tocdepth}{3}\begin{document}\begin{thm}A\end{thm}\begin{pro}B\end{pro}\end{document}