elpa-concurrent software package provides higher level library for concurrent tasks, 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 elpa-concurrent
elpa-concurrent is installed in your system.
Make ensure the elpa-concurrent package were installed using the commands given below,
$ sudo dpkg-query -l | grep elpa-concurrent *
You will get with elpa-concurrent package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Lisp |
| Package | elpa-concurrent |
| Version | 0.4.0-1 |
| Description | higher level library for concurrent tasks |
| Sub Section | Lisp |