apt stuck in weird state that "apt --fix-broken install" won't fix

Question

When trying to sudo apt upgrade I get this:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 emacs25 : Depends: emacs25-common but it is not installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

When I try sudo apt --fix-broken install I get this:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Correcting dependencies... Done
The following additional packages will be installed:
  emacs25-common
The following NEW packages will be installed:
  emacs25-common
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
3 not fully installed or removed.
Need to get 0 B/17,5 MB of archives.
After this operation, 70,3 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
(Reading database ... 226124 files and directories currently installed.)
Preparing to unpack .../emacs25-common_25.3~2.gitc09215a-kk1+18.04_all.deb ...
Unpacking emacs25-common (25.3~2.gitc09215a-kk1+18.04) ...
dpkg: error processing archive /var/cache/apt/archives/emacs25-common_25.3~2.gitc09215a-kk1+18.04_all.deb (--unpack):
 trying to overwrite '/usr/share/emacs/site-lisp/subdirs.el', which is also in package emacs26-common 26.3~1.git96dd019-kk1+18.04
dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
Errors were encountered while processing:
 /var/cache/apt/archives/emacs25-common_25.3~2.gitc09215a-kk1+18.04_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

This is how I installed emacs26:

## Install emacs 26
From <http://ubuntuhandbook.org/index.php/2019/02/install-gnu-emacs-26-1-ubuntu-18-04-16-04-18-10/>:
1. `sudo add-apt-repository ppa:kelleyk/emacs`
1. `sudo apt update && sudo apt install emacs26`

But this is what I get when I try to sudo apt remove emacs26:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 emacs25 : Depends: emacs25-common but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

I found this (Package system is broken. How to fix it?) askubuntu thread with some suggested solutions:

• sudo apt-get -f install result:

  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Correcting dependencies... Done
  The following additional packages will be installed:
  emacs25-common
  The following NEW packages will be installed:
  emacs25-common
  0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
  3 not fully installed or removed.
  Need to get 0 B/17,5 MB of archives.
  After this operation, 70,3 MB of additional disk space will be used.
  Do you want to continue? [Y/n] y
  (Reading database ... 226124 files and directories currently installed.)
  Preparing to unpack .../emacs25-common_25.3~2.gitc09215a-kk1+18.04_all.deb ...
  Unpacking emacs25-common (25.3~2.gitc09215a-kk1+18.04) ...
  dpkg: error processing archive /var/cache/apt/archives/emacs25-common_25.3~2.gitc09215a-kk1+18.04_all.deb (--unpack):
  trying to overwrite '/usr/share/emacs/site-lisp/subdirs.el', which is also in package emacs26-common 26.3~1.git96dd019-kk1+18.04
  dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
  Errors were encountered while processing:
  /var/cache/apt/archives/emacs25-common_25.3~2.gitc09215a-kk1+18.04_all.deb
  E: Sub-process /usr/bin/dpkg returned an error code (1)
  

• sudo dpkg --configure -a result:

  dpkg: dependency problems prevent configuration of emacs25:
   emacs25 depends on emacs25-common; however:
    Package emacs25-common is not installed.
  
  dpkg: error processing package emacs25 (--configure):
   dependency problems - leaving unconfigured
  dpkg: dependency problems prevent configuration of emacs:
   emacs depends on emacs25 | emacs25-lucid | emacs25-nox; however:
    Package emacs25 is not configured yet.
    Package emacs25-lucid is not installed.
    Package emacs25-nox is not installed.
  
  dpkg: error processing package emacs (--configure):
   dependency problems - leaving unconfigured
  dpkg: dependency problems prevent configuration of elpa-async:
   elpa-async depends on emacs; however:
    Package emacs is not configured yet.
  
  dpkg: error processing package elpa-async (--configure):
   dependency problems - leaving unconfigured
  Errors were encountered while processing:
   emacs25
   emacs
   elpa-async
  

• Trying to remove either of those (emacs25, emacs, elpa-async) results in the same:

  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  You might want to run 'apt --fix-broken install' to correct these.
  The following packages have unmet dependencies:
   emacs25 : Depends: emacs25-common but it is not going to be installed
  E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
  

• sudo apt-get clean works without errors but has no effect on any of the above commands.

• Another solution suggested in that thread was to install Synaptic, but sudo apt install synaptic fails like all other apt installs.

Any tips on how I can get out of this weird state? I think that I got into it by cancelling an installation of emacs25 while it was running. I cancelled it because apt was trying to install it as a dependency of something else (elpa-async).