grass70-gui software package provides virtual package provided by grass-gui, 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 grass70-gui
grass70-gui is installed in your system.
Make ensure the grass70-gui package were installed using the commands given below,
$ sudo dpkg-query -l | grep grass70-gui*
You will get with grass70-gui package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Virtual packages |
| Package | grass70-gui |
| Version | |
| Description | virtual package provided by grass-gui |
| Sub Section | Virtual |