/usr/lib/x86_64-linux-gnu/libdap.so.23 is in libdap23 3.18.2-2+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libdap.so.23.1.0
/usr/lib/x86_64-linux-gnu/libdap.so.23.1.0