Consider the following LaTeX2e manuscript

\begin{theorem*}[Hello World]
Hello, world!

When I compile it with pdflatex, the compilation fails with the following error message:

! LaTeX Error: Environment theorem* undefined.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.

l.6 \begin{theorem*}
                    [Hello World]

What is the problem? How can I fix it?

  • 2
    The asterisk?? maybe?
    – Johannes_B
    Nov 12, 2017 at 8:50
  • @Johannes_B: Yes, you're right. I thought the presence of an asterisk is supposed to indicate that the theorem should not be numbered. Apparently this doesn't happen automatically.
    – Evan Aad
    Nov 12, 2017 at 8:52
  • 3
    You can use \newtheoremstyle*{lem}{Lemma}, but the documentation never states that a sudden lem* would work.
    – Johannes_B
    Nov 12, 2017 at 8:54
  • 3
    You can add\newtheorem*{theorem*}{Theorem}to your preamble.
    – Bobyandbob
    Nov 12, 2017 at 8:55
  • @Johannes_B: I thought the asterisk worked like a macro option. I was wrong.
    – Evan Aad
    Nov 12, 2017 at 8:58


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