/usr/include/dune/grid-glue/merging/ is in libdune-grid-glue-dev 2.4.0-1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/dune/grid-glue/merging/computeintersection.cc
/usr/include/dune/grid-glue/merging/computeintersection.hh
/usr/include/dune/grid-glue/merging/conformingmerge.hh
/usr/include/dune/grid-glue/merging/contactmerge.cc
/usr/include/dune/grid-glue/merging/contactmerge.hh
/usr/include/dune/grid-glue/merging/merger.hh
/usr/include/dune/grid-glue/merging/overlappingmerge.cc
/usr/include/dune/grid-glue/merging/overlappingmerge.hh
/usr/include/dune/grid-glue/merging/psurfacemerge.hh
/usr/include/dune/grid-glue/merging/simplexintersection.cc
/usr/include/dune/grid-glue/merging/standardmerge.hh