/usr/include/qhull/QhullSet.h is in libqhull-dev 2015.2-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/qhull/../libqhullcpp/QhullSet.h
/usr/include/qhull/../libqhullcpp/QhullSet.h