/usr/bin/soelim

usage: /usr/bin/soelim [-Crt] [-I dir] [input-file ...]
usage: /usr/bin/soelim {-v | --version}
usage: /usr/bin/soelim --help

GNU soelim eliminates source requests in roff(7) and other text
files; it replaces lines of the form ".so included‐file" within
each text input-file with the contents of included-file recursively,
flattening a tree of documents.  By default, it writes roff "lf"
requests as well to record the name and line number of each
input-file and included-file.  Use the -t option to produce TeX
comments instead of roff requests.  Use the -r option to write
neither.  See the soelim(1) manual page.