/usr/ is in octave-gsl 2.1.0-3.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/x86_64-linux-gnu/
/usr/lib/x86_64-linux-gnu/octave/
/usr/lib/x86_64-linux-gnu/octave/packages/
/usr/lib/x86_64-linux-gnu/octave/packages/gsl-2.1.0/
/usr/lib/x86_64-linux-gnu/octave/packages/gsl-2.1.0/x86_64-pc-linux-gnu-api-v51/
/usr/lib/x86_64-linux-gnu/octave/packages/gsl-2.1.0/x86_64-pc-linux-gnu-api-v51/PKG_ADD
/usr/lib/x86_64-linux-gnu/octave/packages/gsl-2.1.0/x86_64-pc-linux-gnu-api-v51/gsl_sf.oct
/usr/share/
/usr/share/doc/
/usr/share/doc/octave-gsl/
/usr/share/doc/octave-gsl/changelog.Debian.gz
/usr/share/doc/octave-gsl/copyright
/usr/share/octave/
/usr/share/octave/packages/
/usr/share/octave/packages/gsl-2.1.0/
/usr/share/octave/packages/gsl-2.1.0/doc-cache
/usr/share/octave/packages/gsl-2.1.0/gsl_sf_test.m
/usr/share/octave/packages/gsl-2.1.0/packinfo/
/usr/share/octave/packages/gsl-2.1.0/packinfo/DESCRIPTION
/usr/share/octave/packages/gsl-2.1.0/packinfo/INDEX
/usr/share/octave/packages/gsl-2.1.0/packinfo/NEWS
/usr/share/doc/octave-gsl/NEWS