Guide to LaTeX (4th Edition) (Tools and Techniques

414 Appendix C. Error Messages
in math mode and should have been typed here as \_. However, after
the first $ had switched (incorrectly) into math mode, the _ sign became
allowed, with the result that the following letter s was lowered.
If we now correct the text by replacing the $ sign with \$, then the _
symbol is no longer in math mode, producing the error message:
! Missing $ inserted.
$
l.5 ...ice is \$3.50 and the order number is type_
sample.
?
Pressing 〈return〉 here tells T E X to recover from the error by inserting
the apparently missing $ sign at this point before the math command
_. The processing continues, and at some place before the end of the
current paragraph, T E X will notice again that the closing $ is not present.
The same error message is printed as in the first case. The processing
goes on with another 〈return〉 response, with the result:
The price is $3.50 and the order number is typesample.
In all three cases, asking for more help with H would type to the monitor:
I’ve inserted a begin-math/end-math symbol since I think
you left one out. Proceed, with fingers crossed.
The last sentence above is just what we recommend for mathematical
error messages: keep on pressing 〈return〉 or S to get through to the end
of the processing, and then look at the printed output to find the mistake.
C.2.4 Errors from multi-file texts
If the document text is split over many files that are to be read in with
\input or \include commands, the line number in the error message
refers to the file currently being read. A response with E 〈return〉 will call
the editor program and open that file, going to the indicated line where
the error was recognized. With the other responses, the editor has to be
called separately, with the faulty file explicitly named.
It is possible to determine which file was being processed at the time
of the error by examining the processing messages or the.log file. As the
files are opened for reading, T E X writes an opening parenthesis ( and the
name of the file to the monitor and to the transcript.log file. When the
file is closed, a closing parenthesis ) is printed. Output page numbers
are similarly written to both the monitor and transcript file in square
brackets. For example, if the monitor shows the processing messages