First of all, after a upgrade from ubuntu 14.10 to 16.04, I couldn't start X anymore. I thought that must be nvidia-graphics, ok. I went to recovery by root, but the apt-get command was missing libstdc++6 (That was corrupted by the way). So ok, I downloaded the libstdc++6.....deb. I installed it with dpkg -i. Then I could remove nvidia driver and X starts finally. But apt-get couldn't install nothing. dpkg --configure -a says that libstdc++6 and libstdc++6:i386 (?? amd64 here) are broken.
So I removed with all -force --remove -P the libstdc++6.....deb and libstdc++6:i386....deb (I tried to install this .deb too). Then $apt-get doesn't run (error while loading shared libraries: libstdc++.so.6). I've downloaded the libstdc++6.so.6.0.21 (Xenial version) and put it in the /usr/lib/x86_64-linux-gnu/ just to run "apt-get". Now "apt-get install -f" runs but says that a lot of packages depends libstdc++6. Any idea?