@ is a source file cross-reference and listing program written at MIT by
Guy Steele (GLS).  It will cref your assembly language or LISP programs
and produce an output suitable for XGP spooling.  You have the option of
using up to 3 different fonts.  It also has capabilities for listing text
files.

A major feature of @ is the capability to maintain an "LRC" file, which
contains information on how the file was printed along with a checksum of
all the pages in the file.  When you modify the file, you can use this LRC
file to print an update listing of only the pages which have changed.  For
example, the monitor source listing is kept up to date by this method.

@ is run by the system command .@<command line><cr> or by .R ATSIGN<cr>.

Complete information is in ATSIGN.RMS[UP,DOC].