cmucl-source software package provides CMUCL lisp sources, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install cmucl-source
cmucl-source is installed in your system.
Make ensure the cmucl-source package were installed using the commands given below,
$ sudo dpkg-query -l | grep cmucl-source *
You will get with cmucl-source package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Lisp |
| Package | cmucl-source |
| Version | 21a-4 |
| Description | CMUCL lisp sources |
| Sub Section | Lisp |