Unison installation fails and disallows it from working over SSH
If you use Trisquel's Add/Remove applications to install Unison, the installation seems to work fine - no errors are reported, and Unison is added to the accessories menu.
However, Unison fails to sync to a remote machine, reporting to fail to find the unison command.
Sure enough, unison command is not found on either machine. Looking up at Trisquel menu, it turns out that Unison is installed as 'unison-2.51+4.13.1-gtk'. Installation fails to provide an 'unison' alias for that. It seems that without an alias, Unison fails to invoke its counterpart on the remote machine and SSH sync fails.