>I suspect second local installation of gmp/nettle/gnutls in /usr/local.
You're right! root@home:/usr/local/lib# ls -l libgmp* -rw-r--r-- 1 root root 1188388 Jul 22 2017 libgmp.a -rwxr-xr-x 1 root root 914 Jul 22 2017 libgmp.la lrwxrwxrwx 1 root root 16 Jul 22 2017 libgmp.so -> libgmp.so.10.0.5 lrwxrwxrwx 1 root root 16 Jul 22 2017 libgmp.so.10 -> libgmp.so.10.0.5 -rwxr-xr-x 1 root root 482920 Jul 22 2017 libgmp.so.10.0.5 -rw-r--r-- 1 root root 39660 Jul 22 2017 libgmpxx.a -rwxr-xr-x 1 root root 949 Jul 22 2017 libgmpxx.la lrwxrwxrwx 1 root root 17 Jul 22 2017 libgmpxx.so -> libgmpxx.so.4.2.5 lrwxrwxrwx 1 root root 17 Jul 22 2017 libgmpxx.so.4 -> libgmpxx.so.4.2.5 -rwxr-xr-x 1 root root 24704 Jul 22 2017 libgmpxx.so.4.2.5 I have no idea how or why they got installed. Regardless, I've removed them, and "apt --fix-broken install" worked. Thanks! and please close the bug.