/usr/include/singular/singular/Singular/ is in libsingular4-dev-common 1:4.1.0-p3+ds-2build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/singular/singular/Singular/attrib.h
/usr/include/singular/singular/Singular/blackbox.h
/usr/include/singular/singular/Singular/cntrlc.h
/usr/include/singular/singular/Singular/countedref.h
/usr/include/singular/singular/Singular/distrib.h
/usr/include/singular/singular/Singular/eigenval_ip.h
/usr/include/singular/singular/Singular/feOpt.h
/usr/include/singular/singular/Singular/feOptTab.h
/usr/include/singular/singular/Singular/fehelp.h
/usr/include/singular/singular/Singular/fevoices.h
/usr/include/singular/singular/Singular/fglm.h
/usr/include/singular/singular/Singular/gms.h
/usr/include/singular/singular/Singular/grammar.h
/usr/include/singular/singular/Singular/idrec.h
/usr/include/singular/singular/Singular/ipconv.h
/usr/include/singular/singular/Singular/ipid.h
/usr/include/singular/singular/Singular/ipprint.h
/usr/include/singular/singular/Singular/ipshell.h
/usr/include/singular/singular/Singular/libparse.h
/usr/include/singular/singular/Singular/libsingular.h
/usr/include/singular/singular/Singular/linearAlgebra_ip.h
/usr/include/singular/singular/Singular/links/
/usr/include/singular/singular/Singular/links/dbm_sl.h
/usr/include/singular/singular/Singular/links/ndbm.h
/usr/include/singular/singular/Singular/links/pipeLink.h
/usr/include/singular/singular/Singular/links/silink.h
/usr/include/singular/singular/Singular/links/simpleipc.h
/usr/include/singular/singular/Singular/links/sing_dbm.h
/usr/include/singular/singular/Singular/links/slInit.h
/usr/include/singular/singular/Singular/links/ssiLink.h
/usr/include/singular/singular/Singular/lists.h
/usr/include/singular/singular/Singular/locals.h
/usr/include/singular/singular/Singular/maps_ip.h
/usr/include/singular/singular/Singular/misc_ip.h
/usr/include/singular/singular/Singular/mmalloc.h
/usr/include/singular/singular/Singular/mod_lib.h
/usr/include/singular/singular/Singular/newstruct.h
/usr/include/singular/singular/Singular/number2.h
/usr/include/singular/singular/Singular/pcv.h
/usr/include/singular/singular/Singular/pyobject_setup.h
/usr/include/singular/singular/Singular/sdb.h
/usr/include/singular/singular/Singular/stype.h
/usr/include/singular/singular/Singular/subexpr.h
/usr/include/singular/singular/Singular/table.h
/usr/include/singular/singular/Singular/tok.h
/usr/include/singular/singular/Singular/walk.h