$ sudo apt-get -o Debug::pkgProblemResolver=yes install xorg
Reading package lists... Done
Building dependency tree
Reading state information... Done
Starting
Starting 2
Investigating (0) libgl1-mesa-dri-lts-quantal [ amd64 ] < 9.0.3-0ubuntu0.1~precise2 > ( libs )
Broken libgl1-mesa-dri-lts-quantal:amd64 Conflicts on libgl1-mesa-dri [ amd64 ] < none -> 9.0.3-0ubuntu0.1 > ( libs )
  Considering libgl1-mesa-dri:amd64 9 as a solution to libgl1-mesa-dri-lts-quantal:amd64 10
  Added libgl1-mesa-dri:amd64 to the remove list
  Conflicts//Breaks against version 9.0-0ubuntu1 for libgl1-mesa-dri but that is not InstVer, ignoring
  Fixing libgl1-mesa-dri-lts-quantal:amd64 via keep of libgl1-mesa-dri:amd64
Investigating (0) xserver-xorg-lts-quantal [ amd64 ] < 1:7.7+1ubuntu4~precise1 > ( x11 )
Broken xserver-xorg-lts-quantal:amd64 Conflicts on xserver-xorg [ amd64 ] < none -> 1:7.7+1ubuntu4 > ( x11 )
  Considering xserver-xorg:amd64 11 as a solution to xserver-xorg-lts-quantal:amd64 7
  Removing xserver-xorg-lts-quantal:amd64 rather than change xserver-xorg:amd64
Investigating (0) xserver-xorg-core-lts-quantal [ amd64 ] < 2:1.13.0-0ubuntu6.1~precise3 > ( x11 )
Broken xserver-xorg-core-lts-quantal:amd64 Conflicts on xserver-xorg-core [ amd64 ] < none -> 2:1.13.0-0ubuntu6.2 > ( x11 )
  Considering xserver-xorg-core:amd64 4 as a solution to xserver-xorg-core-lts-quantal:amd64 5
  Added xserver-xorg-core:amd64 to the remove list
  Conflicts//Breaks against version 2:1.13.0-0ubuntu6 for xserver-xorg-core but that is not InstVer, ignoring
  Fixing xserver-xorg-core-lts-quantal:amd64 via keep of xserver-xorg-core:amd64
Investigating (1) xserver-xorg [ amd64 ] < none -> 1:7.7+1ubuntu4 > ( x11 )
Broken xserver-xorg:amd64 Depends on xserver-xorg-core [ amd64 ] < none -> 2:1.13.0-0ubuntu6.2 > ( x11 ) (>= 2:1.11)
  Considering xserver-xorg-core:amd64 4 as a solution to xserver-xorg:amd64 11
  Holding Back xserver-xorg:amd64 rather than change xserver-xorg-core:amd64
Investigating (2) xorg [ amd64 ] < 1:7.6+12ubuntu2 -> 1:7.7+1ubuntu4 > ( x11 )
Broken xorg:amd64 Depends on xserver-xorg [ amd64 ] < none -> 1:7.7+1ubuntu4 > ( x11 ) (>= 1:7.7+1ubuntu4)
  Considering xserver-xorg:amd64 11 as a solution to xorg:amd64 10001
  Re-Instated xserver-xorg-core:amd64
  Re-Instated xserver-xorg:amd64
Investigating (2) xserver-xorg-core-lts-quantal [ amd64 ] < 2:1.13.0-0ubuntu6.1~precise3 > ( x11 )
Broken xserver-xorg-core-lts-quantal:amd64 Conflicts on xserver-xorg-core [ amd64 ] < none -> 2:1.13.0-0ubuntu6.2 > ( x11 )
  Considering xserver-xorg-core:amd64 4 as a solution to xserver-xorg-core-lts-quantal:amd64 5
  Added xserver-xorg-core:amd64 to the remove list
  Conflicts//Breaks against version 2:1.13.0-0ubuntu6 for xserver-xorg-core but that is not InstVer, ignoring
  Fixing xserver-xorg-core-lts-quantal:amd64 via keep of xserver-xorg-core:amd64
Investigating (3) xserver-xorg [ amd64 ] < none -> 1:7.7+1ubuntu4 > ( x11 )
Broken xserver-xorg:amd64 Depends on xserver-xorg-core [ amd64 ] < none -> 2:1.13.0-0ubuntu6.2 > ( x11 ) (>= 2:1.11)
  Considering xserver-xorg-core:amd64 5 as a solution to xserver-xorg:amd64 11
  Holding Back xserver-xorg:amd64 rather than change xserver-xorg-core:amd64
Investigating (4) xorg [ amd64 ] < 1:7.6+12ubuntu2 -> 1:7.7+1ubuntu4 > ( x11 )
Broken xorg:amd64 Depends on xserver-xorg [ amd64 ] < none -> 1:7.7+1ubuntu4 > ( x11 ) (>= 1:7.7+1ubuntu4)
  Considering xserver-xorg:amd64 11 as a solution to xorg:amd64 10001
Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 xorg : Depends: xserver-xorg (>= 1:7.7+1ubuntu4)
E: Unable to correct problems, you have held broken packages.