emerge kuser
Calculating dependencies
Parse Error reading PROVIDE and USE in '/var/db/pkg/x11-base/xorg-x11-6.8.2-r6'
Possibly Invalid: 'virtual/x11 opengl? virtual/opengl opengl? virtual/glu virtual/xft'
Exception: Conditional without parenthesis: 'opengl?'

... done!

!!! Error: the <=x11-base/xorg-x11-6.9 package conflicts with another package;
!!!        the two packages cannot be installed on the same system together.
!!!        Please use 'emerge --pretend' to determine blockers.

For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked