# latex reference

LaTeX Warning: Reference 2.20' on page 57 undefined on input line 2685.

I don't know about what this warning is. What this warning means? My code is too long and I make

\begin{thm}\label{2.20}


at line 2185 and

\autoref{2.20}


at line 2715. And I even use \usepackage{hyperref}

• Welcome to TeX.SX. Have you compiled to pdf several times? – Johannes_B Feb 2 at 6:19
• With just the information given, we can only guess that there is something in your document, that causes an issue. But without a crystall ball, we cannot give any further hints. We would need to see a minimal working example. Probably will take 30 to 60 minutes to prepare one for a document that big. – Johannes_B Feb 2 at 6:24
• Ok. Let's assume Theorem 2.20 is about the Wombat Theorem. A good label for that would be thm:wombat. You can later reference to it with thm:wombat. LaTeX will figure out the correct number for you. – Johannes_B Feb 2 at 6:29
• The code shown so far looks like it should work. But Johannes is absolutely right, you should avoid nondescript label names like 2.20 (which could be really confusing if you reorder stuff and it comes out as 2.21 in the document!) and try to use more relevant names like thm:liouville or thm:bddfunction. With this issue we can only help further if you show us a small example document of what you are doing, a so-called MWE (tex.meta.stackexchange.com/q/228/35864). – moewe Feb 2 at 7:07
• What are you using to compile? Could you be deleting your .aux? Is this something that happens with this single \label-\ref`, or with others as well? Ultimately, we need to be able to replicate the problem... so how can we do that? – Werner Feb 2 at 7:17