Gentoo-Tux ~ # emerge -avuD world

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

Calculating world dependencies... done!
[ebuild     U ] app-admin/python-updater-0.3 [0.2] 3 kB
[ebuild  N    ] app-emulation/emul-linux-x86-compat-1.0-r3  0 kB
[ebuild     U ] sys-apps/usbutils-0.73 [0.72-r4] USE="zlib%* -network-cron" 170 kB
[ebuild     U ] sys-devel/gdb-6.7.1 [6.7] USE="nls -test -vanilla" 14,741 kB
[ebuild     U ] net-libs/libsoup-2.2.103 [2.2.102] USE="ssl -debug -doc" 484 kB
[ebuild     U ] dev-cpp/libxmlpp-2.20.0-r1 [2.20.0] USE="-debug -doc" 0 kB
[ebuild     U ] dev-cpp/gtkmm-2.12.1 [2.12.0] USE="-accessibility -debug -doc -examples" 13,014 kB
[ebuild     U ] net-nds/openldap-2.3.39 [2.3.38] USE="berkdb crypt gdbm ipv6 kerberos perl readline ssl tcpd -debug -minimal -odbc -overlays -samba -sasl (-selinux) -slp -smbkrb5passwd" 3,719 kB
[ebuild     U ] dev-lang/ocaml-3.09.3-r2 [3.09.3-r1] USE="X gdbm ncurses -emacs% -latex -tk -xemacs%" 0 kB
[ebuild     U ] dev-ml/lablgtk-2.10.0 [2.6.0] USE="opengl spell%* svg -debug -doc -glade -gnome -gnomecanvas -sourceview%" 725 kB
[ebuild     U ] net-misc/unison-2.17.1-r1 [2.13.16] USE="gtk threads -debug -doc -static" 0 kB
[blocks B     ] =sys-devel/gcc-3.3* (is blocking app-emulation/emul-linux-x86-compat-1.0-r3)

Total: 11 packages (10 upgrades, 1 new, 1 block), Size of downloads: 32,853 kB

!!! 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

Gentoo-Tux ~ # equery depends emul-linux-x86-compat
[ Searching for packages depending on emul-linux-x86-compat... ]
app-arch/rar-3.7.1 (amd64? app-emulation/emul-linux-x86-compat)