# emerge -uDNav --with-bdeps=y --verbose-conflicts --keep-going --backtrack=90 system world
These are the packages that would be merged, in order:
Calculating dependencies... done!
[ebuild N ~] media-sound/jack2-1.9.11_rc1:2::gentoo USE="alsa dbus pam readline -celt -classic -doc -libsamplerate -opus -sndfile" ABI_X86="32 (64) (-x32)" PYTHON_TARGETS="python2_7" 6.330 KiB
[ebuild U ~] media-sound/jack-audio-connection-kit-9998::proaudio [0.125.0::gentoo] USE="alsa pam (-altivec) (-coreaudio) -dbus% -debug -doc -examples -oss" ABI_X86="32 (64) (-x32)" CPU_FLAGS_X86="sse -3dnow" 0 KiB
[blocks B ] media-sound/jack-audio-connection-kit:0 ("media-sound/jack-audio-connection-kit:0" is blocking media-sound/jack2-1.9.11_rc1)
Total: 2 packages (1 upgrade, 1 new), Size of downloads: 6.330 KiB
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-sound/jack-audio-connection-kit-9998:0/0::proaudio, ebuild scheduled for merge) pulled in by
media-sound/jack-audio-connection-kit:= required by (media-sound/rosegarden-17.04:0/0::gentoo, installed)
>=media-sound/jack-audio-connection-kit-0.100 required by (media-libs/xine-lib-1.2.6-r2:1/1::gentoo, installed)
media-sound/jack-audio-connection-kit:0/0= required by (media-sound/rosegarden-17.04:0/0::gentoo, installed)
>=media-sound/jack-audio-connection-kit-0.121.3 required by (media-libs/mlt-6.4.1-r2:0/0::gentoo, installed)
media-sound/jack-audio-connection-kit required by (media-sound/timidity++-2.14.0-r2:0/0::gentoo, installed)
>=media-sound/jack-audio-connection-kit-0.80.0 required by (media-sound/jamin-0.95.0-r2:0/0::gentoo, installed)
>=media-sound/jack-audio-connection-kit-0.121.3-r1[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_ppc_32(-)?,abi_ppc_64(-)?,abi_s390_32(-)?,abi_s390_64(-)?] (>=media-sound/jack-audio-connection-kit-0.121.3-r1[abi_x86_32(-),abi_x86_64(-)]) required by (virtual/jack-0:0/0::gentoo, installed)