I made a terrible mistake and upgraded to 18.04 without making a backup in a different partition by doing:
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo apt-get autoremove
sudo apt install update-manager-core
sudo do-release-upgrade -d
Then I did update and upgrade commands after a restart. There are now many issues with unmet dependencies and broken packages that the sudo apt-get -f install commands cannot fix. UPDATE  The first part of the output from the sudo apt install -f error log is:
    Reading package lists...
Building dependency tree...
Reading state information...
Correcting dependencies... failed.
The following packages have unmet dependencies:
 gnome-calendar : Depends: gsettings-desktop-schemas (>= 3.21.2) but 3.18.1-1ubuntu1 is installed
 gnome-session : Depends: gnome-shell (>= 3.25.91-0ubuntu4~) but it is not installed
                 Depends: gnome-session-bin (>= 3.28.1-0ubuntu2) but 3.18.1.2-1ubuntu1.16.04.2 is installed
                 Depends: gnome-session-common (= 3.28.1-0ubuntu2) but 3.18.1.2-1ubuntu1.16.04.2 is installed
                 Depends: xwayland but it is not installed
                 Recommends: fonts-cantarell but it is not installed
                 Recommends: adwaita-icon-theme-full
                 Recommends: gnome-themes-extra but it is not installed
 gnome-settings-daemon : Depends: libgnome-desktop-3-17 (>= 3.17.92) but it is not installed
                         Depends: gsettings-desktop-schemas (>= 3.20) but 3.18.1-1ubuntu1 is installed
 hplip : Depends: python3 (< 3.6) but 3.6.5-3 is installed
 libc-dev-bin : Depends: libc6 (< 2.24) but 2.27-3ubuntu1 is installed
 libc6-dbg : Depends: libc6 (= 2.23-0ubuntu10) but 2.27-3ubuntu1 is installed
 libc6-dev : Depends: libc6 (= 2.23-0ubuntu10) but 2.27-3ubuntu1 is installed
 libgmime-3.0-0 : Depends: libgpgme11 (>= 1.7.0) but 1.6.0-1 is installed
 libreoffice-avmedia-backend-gstreamer : Depends: libreoffice-core (= 1:5.1.6~rc2-0ubuntu1~xenial3) but 1:6.0.3-0ubuntu1 is installed
 libreoffice-base-core : Depends: libreoffice-core (= 1:5.1.6~rc2-0ubuntu1~xenial3) but 1:6.0.3-0ubuntu1 is installed
 libreoffice-calc : Depends: libreoffice-base-core (= 1:6.0.3-0ubuntu1) but 1:5.1.6~rc2-0ubuntu1~xenial3 is installed
                    Depends: liborcus-0.13-0 (>= 0.13.3) but it is not installed
 libreoffice-core : Depends: libgpgmepp6 (>= 1.10.0) but it is not installed
                    Depends: liborcus-0.13-0 (>= 0.13.3) but it is not installed
                    Depends: libpoppler73 (>= 0.62.0) but it is not installed
                    Depends: libxmlsec1 (>= 1.2.25) but it is not installed
                    Depends: libxmlsec1-nss (>= 1.2.25) but it is not installed
 libreoffice-gnome : Depends: libreoffice-gtk3 but it is not installed
 libreoffice-gtk : Depends: libreoffice-gtk2 but it is not installed
 libreoffice-math : Depends: libreoffice-core (= 1:5.1.6~rc2-0ubuntu1~xenial3) but 1:6.0.3-0ubuntu1 is installed
 libreoffice-writer : Depends: libreoffice-base-core (= 1:6.0.3-0ubuntu1) but 1:5.1.6~rc2-0ubuntu1~xenial3 is installed
                      Depends: libabw-0.1-1 but it is not installed
                      Depends: libepubgen-0.1-1 (>= 0.1.0) but it is not installed
 libtotem0 : Depends: libgnome-desktop-3-17 (>= 3.17.92) but it is not installed
 libwayland-egl1-mesa : Depends: libegl1 but it is not installed
 libwebkitgtk-1.0-0 : Depends: libjavascriptcoregtk-1.0-0 (= 2.4.11-0ubuntu0.1) but 2.4.11-3ubuntu3 is installed
                      Depends: libwebkitgtk-1.0-common (>= 2.4.11) but it is not installable
 nautilus : Depends: libgnome-desktop-3-17 (>= 3.18.1) but it is not installed
 python3-brlapi : Depends: python3 (< 3.6) but 3.6.5-3 is installed
 python3-cffi-backend : Depends: python3 (< 3.6) but 3.6.5-3 is installed
 python3-crypto : Depends: python3 (< 3.6) but 3.6.5-3 is installed
and
E: Error, pkgProblemResolver::Resolve generated breaks,   
this may be caused by held packages.  
Trying to fix broken packages in Synaptic produces this error message:
E: Error, pkgProblemResolver::Resolve generated breaks,   
this may be caused by held packages.     
It doesn't look like there's anything wrong with the sources.list file, and it appears to have been updated when I tried the install. I barely know what I'm doing and am happy to provide more detail on error messages. If there's a way to enable scrolling up in xterm, which is what I'm now using since Gnome terminal can't be opened.
I'd like to remove all 47 broken packages and held packages, reinstall them correctly or not install them for now if that's an option (i.e., for things like LibreOffice, which isn't a current need), and be able to use the Gnome terminal.
I'm looking for beginner steps for how to fix all these problems. Is there a guide about how to start? An obvious post that I have missed in my searches for answers? I think this post is heading in the right direction, but it is a little over my head. Any help is much appreciated. I am wondering if it would be genuinely easier to start from a fresh 16.04 install.
 
     
     
     
     
     
     
     
     
     
     
     
     
    