dependency not met

You should upgrade all packages together, not individually.
You appear to be trying to install packages from artful-proposed, which is not recommended for daily use, unless you are testing SRU fixes.
If you do not intend to validate pre-release test packages, please disable artful-proposed on your system.

Incorrect. I am *_not_* installing packages from artful-proposed. I do *_not_* upgrade packages individually.
Here is my sources.list:
deb http://ca.archive.ubuntu.com/ubuntu/ artful main restricteddeb http://ca.archive.ubuntu.com/ubuntu/ artful-updates main restricteddeb http://ca.archive.ubuntu.com/ubuntu/ artful universedeb http://ca.archive.ubuntu.com/ubuntu/ artful-updates universedeb http://ca.archive.ubuntu.com/ubuntu/ artful multiversedeb http://ca.archive.ubuntu.com/ubuntu/ artful-updates multiversedeb http://ca.archive.ubuntu.com/ubuntu/ artful-backports main restricted universe multiversedeb http://archive.canonical.com/ubuntu artful partnerdeb http://security.ubuntu.com/ubuntu artful-security main restricteddeb http://security.ubuntu.com/ubuntu artful-security universedeb http://security.ubuntu.com/ubuntu artful-security multiversedeb http://www.duinsoft.nl/pkg debs all
This is the update alias which I run daily (and which is throwing the errors which I have reported):
sudo apt-get update && sudo aptitude --with-recommends safe-upgrade && sudo aptitude --with-recommends full-upgrade && sudo apt-get upgrade && sudo apt-get dist-upgrade && sudo apt autoremove && sudo aptitude autoclean

      From: Dimitri John Ledkov <email address hidden>
 To: <email address hidden>
 Sent: Tuesday, December 12, 2017 5:50 AM
 Subject: [Bug 1737318] Re: dependency not met

You should upgrade all packages together, not individually.
You appear to be trying to install packages from artful-proposed, which is not recommended for daily use, unless you are testing SRU fixes.
If you do not intend to validate pre-release test packages, please disable artful-proposed on your system.

** Changed in: systemd (Ubuntu)
      Status: New => Invalid

--
You received this bug notification because you are subscribed to the bug
report.
https://bugs.launchpad.net/bugs/1737318

Title:
  dependency not met

Status in systemd package in Ubuntu:
  Invalid

Bug description:
  The following packages have unmet dependencies:
  libnss-resolve : Depends: systemd (= 234-2ubuntu12.1) but 234-2ubuntu12.2 is to be installed
  open: 23; closed: 490; defer: 5; conflict: 5                                                                                                                                                                      .The following actions will resolve these dependencies:

      Keep the following packages at their current version:
  1)    libpam-systemd [234-2ubuntu12.1 (artful-security, artful-updates, now)]
  2)    libsystemd0 [234-2ubuntu12.1 (artful-security, artful-updates, now)]
  3)    systemd [234-2ubuntu12.1 (artful-security, artful-updates, now)]

  ProblemType: Bug
  DistroRelease: Ubuntu 17.10
  Package: libnss-resolve 234-2ubuntu12.1
  ProcVersionSignature: Ubuntu 4.13.0-19.22-generic 4.13.13
  Uname: Linux 4.13.0-19-generic x86_64
  ApportVersion: 2.20.7-0ubuntu3.6
  Architecture: amd64
  CurrentDesktop: Unity:Unity7:ubuntu
  Date: Sat Dec  9 07:40:09 2017
  InstallationDate: Installed on 2016-10-02 (432 days ago)
  InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160512)
  SourcePackage: systemd
  Upgra...

Sorry for the poorly formatted reply. In future, I will not use a webmail client tto send bugmail.

If you didn't install these packages from artful-proposed, and you don't have artful-proposed configured in your sources.list, why is apt reporting to you that it is installing a version of systemd that is only published in artful-proposed?

What is the output of 'apt policy systemd'?

[Expired for systemd (Ubuntu) because there has been no activity for 60 days.]