::
Manuale di [tt]amsthm[/tt]
`\newtheorem{thm}{Theorem}
\newtheorem{lem}[thm]{Lemma}`
The optional argument [tt][thm][/tt] in the second statement means that the [tt]lem[/tt] environ-
ment should share the [tt]thm[/tt] numbering sequence instead of having its own independent
sequence.
