Remove section numbers latex

Question

I have a problem with section numbering in latex. I want to remove the section numbers from headings and contents but I want the numbers to be there for lemmas, theorems etc. I want it to look like:

 Section Whatever
   Some unimportant text.

 Section Whatever else
   Another unimportant text.
   Lemma 2.1
   Theorem 2.2 

 Section Whatever again
   Theorem 3.1

How can I do it? I tried

 \renewcommand\thesection{}

but it removes the numbers even from lemmas and theorems. Thank you very much :)

Answer 1

Under the default article class we can merely remove the formatting applied to the section counter by adding

\makeatletter
\renewcommand{\@seccntformat}[1]{}
\makeatother

to the preamble. This will remove all sectional title numbering (\sections, \subsections, \subsubsections, ...), yet keep them where they are references or whenever \thesection is used.

\documentclass{article}

\newtheorem{theorem}{Theorem}[section]% Theorems numbered by section
\newtheorem{lemma}[theorem]{Lemma}% Lemma uses theorem's counter

\makeatletter
\renewcommand{\@seccntformat}[1]{}
\makeatother

\begin{document}

\section{Section whatever}
Some uninportant text.

\section{Section whatever else}
Another uninportant text.

\begin{lemma}
Some lemma.
\end{lemma}

\begin{theorem}
Some theorem.
\end{theorem}

\section{Section whatever again}
\begin{theorem}
Another theorem.
\end{theorem}

\end{document}