agda-mode software package provides transitional dummy package for elpa-agda2-mode, 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 agda-mode
agda-mode is installed in your system.
Make ensure the agda-mode package were installed using the commands given below,
$ sudo dpkg-query -l | grep agda-mode *
You will get with agda-mode package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Miscellaneous |
| Package | agda-mode |
| Version | 2.5.1-2 |
| Description | transitional dummy package for elpa-agda2-mode |
| Sub Section | Miscellaneous |