These are the packages that would be merged, in order:

Calculating dependencies ...

!!! Problem resolving dependencies for =x11-wm/mutter-50.5
 done!
Dependency resolution took 0.82 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=x11-wm/mutter-50.5" has unmet requirements.
- x11-wm/mutter-50.5::gentoo USE="(xwayland) -bash-completion -debug -devkit -elogind -gnome -gtk-doc -introspection -screencast (-selinux) -sysprof (-systemd) -test" INPUT_DEVICES="-wacom" VIDEO_CARDS="-nvidia"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( elogind systemd )

  The above constraints are a subset of the following complete expression:
    devkit? ( screencast ) gtk-doc? ( introspection ) exactly-one-of ( elogind systemd ) test? ( screencast )