The LICENSE.txt file summarizes the general simh license which is 
essentially stated at the top of all source code files, along with 
some additional limitations spelled out in the LICENSE.txt file.

The purpose of this COPYING.txt file is to provide guidance for folks 
who may want to include some or all of the simh code in other projects.
The point of this guidance is so that the actual version of the simh 
code is retained in whatever derivative work may be produced so that 
problems may be reasonably reported AND so that users and developers 
can easily determine what simh version they are working with.

The best way to do this leverages git's archive feature which in 
the simh case has simh git commit information embedded in the archive.
Alternatively, some live git operations could be done to fetch and
extrace the current commit/version information from that archive 
and then pass it around and through the derivative project's build 
mechanism.

GIT ARCHIVE CONSIDERATIONS:

For all projects (even those where Internet connectivity may not be
available on all machines that may build the project) the git archive 
feature would be most appropriate.  
Additionally a few dozen megabytes of storage on the build machine 
won't be needed to hold the complete simh codebase.  These days 
storage is so cheap that this generally shouldn't be a concern, but
some folks really like to keep things to a minimal footprint.

A git archive containing all of the simh components can be acquired
from the simh gitub repository for the latest simh code from:
        https://github.com/simh/simh/archive/master.zip
or for a specific simh commit:
        https://github.com/simh/simh/archive/<commit-hash>.zip
        
The archive produced will automatically contain the specifics of the 
simh git version that has been archived.

Each time the simh components are acquired as an archive, the 
project's interesting simh pieces can then be extracted from the 
archive, modified as needed by that project and the project's build 
mechanism can then compile the simh components with:

    -DSIM_VERSION_MODE=derivative-project-name-and-or-version

This will result in simulators built this way to have SHOW VERSION 
output both identifying the particular version of simh pieces that 
were used as well as whatever interesting version the project may 
want to identify itself with.

Those acquired and extracted pieces can then be stored in the source 
code system for the derivative project and potentially be updated 
from time to time.

If all of the simh components aren't going to be available in the 
derivative project, all of the actual simulator pieces should generally
be gathered and used within the derivative project.  These pieces 
should certainly include all the source code (and license files) in 
the root simh directory along with the particular simulator's source 
directory, and any additional directories which may be referenced in 
the normal simulator build.  These additional directories may include:
display, slirp and slirp_glue.

DIRECT GIT repository access

Using a direct git approach is more complicated and entangles 
capturing the git commit id and time and passing that around and 
through the derivative project's build mechanisms and the working
environment available in the derivative project.  Folks going down 
this path are on their own to try to solve this.