/usr/lib/x86_64-linux-gnu/libdeal.ii.so is in libdeal.ii-dev 8.1.0-6ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libdeal.ii.so.8.1.0
/usr/lib/x86_64-linux-gnu/libdeal.ii.so.8.1.0