/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/ is in libslepc-complex-3.7.3-dev 3.7.3+dfsg1-5.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/bvimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/dsimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/epsimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/fnimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/mfnimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/nepimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/pepimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/rgimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/slepcimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/stimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/svdimpl.h
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/private/vecimplslepc.h