/usr/share/common-lisp/systems/cl-interpol.asd is in cl-interpol 0.2.6-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/common-lisp/systems/../source/cl-interpol/cl-interpol.asd
/usr/share/common-lisp/systems/../source/cl-interpol/cl-interpol.asd