/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/ is in libslepc3.6.1-dbg 3.6.1.dfsg1-2build2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcbv.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcbvdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcds.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcdsdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepceps.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcepsdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcfn.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcfndef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcmfn.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcmfndef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcnep.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcnepdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcpep.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcpepdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcrg.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcrgdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcst.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcstdef.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcsvd.h90
/usr/lib/slepcdir/3.6.1/x86_64-linux-gnu-real-debug/include/slepc/finclude/ftn-custom/slepcsvddef.h90