darkr dwhelper # emerge -pv libpng

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

Calculating dependencies... done!
[ebuild   R   ~] media-libs/libpng-1.5.5  USE="apng -static-libs" 0 kB
[blocks B      ] <x11-libs/gdk-pixbuf-2.24.0-r1 ("<x11-libs/gdk-pixbuf-2.24.0-r1" is blocking media-libs/libpng-1.5.5)

Total: 1 package (1 reinstall), Size of downloads: 0 kB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (media-libs/libpng-1.5.5::gentoo, ebuild scheduled for merge) pulled in by
    libpng


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


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