For some purpose I need the "database_gap" extension package which has to be installed separately. This, however, is a huge problem to me. I tried to implement every piece of advice I could find in this forum or elsewhere on the internet. First, I typed install_package(package="database_gap") into the notebook and was told to use the shell prompt instead (Run 'sage -i database_gap' from a shell prompt instead). I then used the Windows command line to access the folder of virtualbox (C:/program files/Oracle/virtualbox) and typed in just that. Syntax error ("Command doesn't exist"). I then tried several variations, e.g. I put in the word VBoxManage at the beginning of the command, replaced Sage by Sage-6.9 and database_gap by database_gap-4.7.8 (which is the actual name of the package folder which I downloaded). Nothing worked.