(latex2e.info)Cross references

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7 Cross references
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We often want something like 'See Theorem~31'.  But by-hand typing the
31 is poor practice.  Instead you should write a "label" such as
'\label{eq:GreensThm}' and then "reference" it, as with 'See
equation~\ref{eq:GreensThm}'.  LaTeX will automatically work out the
number, put it into the output, and will change that number later if
needed.

     We will see this with Theorem~\ref{th:GreensThm}. % forward reference
     ...
     \begin{theorem} \label{th:GreensThm}
       ...
     \end{theorem}
     ...
     See Theorem~\ref{th:GreensThm} on page~\pageref{th:GreensThm}.

   LaTeX tracks cross reference information in a file having the
extension '.aux' and with the same base name as the file containing the
'\label'.  So if '\label' is in 'calculus.tex' then the information is
in 'calculus.aux'.  LaTeX puts the information in that file every time
it runs across a '\label'.

   The behavior described in the prior paragraph results in a quirk that
happens when your document has a "forward reference", a '\ref' that
appears before the associated '\label'.  If this is the first time that
you are compiling the document then you will get 'LaTeX Warning:
Label(s) may have changed. Rerun to get cross references right' and in
the output the forward reference will appear as two question marks '??',
in boldface.  A similar thing happens if you change some things so the
references changes; you get the same warning and the output contains the
old reference information.  In both cases, resolve this by compiling the
document a second time.

   The 'cleveref' package enhances LaTeX's cross referencing features.
You can arrange that if you enter
'\begin{thm}\label{th:Nerode}...\end{thm}' then '\cref{th:Nerode}' will
output 'Theorem 3.21', without you having to enter the "Theorem."

\label

Assign a symbolic name to a piece of text.

\pageref

Refer to a page number.

\ref

Refer to a section, figure or similar.