localhost ~ #  emerge sabayon-sources
Calculating dependencies... done!
[ebuild  N    ] sys-kernel/sabayon-sources-2.6.23-r1  USE="symlink -build"
[blocks B     ] =sys-kernel/sabayon-sources-2.6.23-r1 (is blocking sys-kernel/linux-sabayon-2.6.23-r1)

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

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

localhost ~ #