This is on a vanilla Leap 42.3 VM in OpenStack (using a very recent Leap 42.3
OpenStack image from OBS):

libudev1 in installed (it's part of the base system). Notice the version number
228-26.4

target137074025075:/home/ubuntu # zypper up libudev1
Loading repository data...
Reading installed packages...
No update candidate for 'libudev1-228-26.4.x86_64'. The highest available
version is already installed.
Resolving package dependencies...

Nothing to do.

In order to build something from source, I need libudev-devel. But it cannot be
installed without first downgrading libudev1:

target137074025075:/home/ubuntu # zypper in libudev-devel
Loading repository data...
Reading installed packages...
Resolving package dependencies...

Problem: libudev-devel-228-26.3.x86_64 requires libudev1 = 228-26.3, but this
requirement cannot be provided
  uninstallable providers: libudev1-228-26.3.x86_64[openSUSE-Leap-42.3-Oss]
 Solution 1: downgrade of libudev1-228-26.4.x86_64 to libudev1-228-26.3.x86_64
 Solution 2: do not install libudev-devel-228-26.3.x86_64
 Solution 3: break libudev-devel-228-26.3.x86_64 by ignoring some of its
dependencies

Choose from above solutions by number or cancel [1/2/3/c] (c):