/usr/include/gpp4/ is in libgpp4-dev 1.3.1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gpp4/ccp4/
/usr/include/gpp4/ccp4/ccp4_array.h
/usr/include/gpp4/ccp4/ccp4_errno.h
/usr/include/gpp4/ccp4/ccp4_file_err.h
/usr/include/gpp4/ccp4/ccp4_fortran.h
/usr/include/gpp4/ccp4/ccp4_general.h
/usr/include/gpp4/ccp4/ccp4_parser.h
/usr/include/gpp4/ccp4/ccp4_program.h
/usr/include/gpp4/ccp4/ccp4_spg.h
/usr/include/gpp4/ccp4/ccp4_sysdep.h
/usr/include/gpp4/ccp4/ccp4_types.h
/usr/include/gpp4/ccp4/ccp4_unitcell.h
/usr/include/gpp4/ccp4/ccp4_utils.h
/usr/include/gpp4/ccp4/ccp4_vars.h
/usr/include/gpp4/ccp4/cmap_data.h
/usr/include/gpp4/ccp4/cmap_errno.h
/usr/include/gpp4/ccp4/cmap_header.h
/usr/include/gpp4/ccp4/cmap_labels.h
/usr/include/gpp4/ccp4/cmap_skew.h
/usr/include/gpp4/ccp4/cmap_stats.h
/usr/include/gpp4/ccp4/cmaplib.h
/usr/include/gpp4/ccp4/cmaplib_f.h
/usr/include/gpp4/ccp4/cmtzlib.h
/usr/include/gpp4/ccp4/csymlib.h
/usr/include/gpp4/ccp4/cvecmat.h
/usr/include/gpp4/ccp4/library_file.h
/usr/include/gpp4/ccp4/mtzdata.h
/usr/include/gpp4/ccp4/overview.h
/usr/include/gpp4/ccp4/pack_c.h
/usr/include/gpp4/ccp4/symlib.h