/usr/include/singular/singular/coeffs/ 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/coeffs/AE.h
/usr/include/singular/singular/coeffs/AEQ.h
/usr/include/singular/singular/coeffs/AEp.h
/usr/include/singular/singular/coeffs/Enumerator.h
/usr/include/singular/singular/coeffs/OPAE.h
/usr/include/singular/singular/coeffs/OPAEQ.h
/usr/include/singular/singular/coeffs/OPAEp.h
/usr/include/singular/singular/coeffs/bigintmat.h
/usr/include/singular/singular/coeffs/coeffs.h
/usr/include/singular/singular/coeffs/ffields.h
/usr/include/singular/singular/coeffs/flintcf_Q.h
/usr/include/singular/singular/coeffs/flintcf_Zn.h
/usr/include/singular/singular/coeffs/gnumpc.h
/usr/include/singular/singular/coeffs/gnumpfl.h
/usr/include/singular/singular/coeffs/longrat.h
/usr/include/singular/singular/coeffs/modulop.h
/usr/include/singular/singular/coeffs/mpr_complex.h
/usr/include/singular/singular/coeffs/mpr_global.h
/usr/include/singular/singular/coeffs/numbers.h
/usr/include/singular/singular/coeffs/numstats.h
/usr/include/singular/singular/coeffs/rintegers.h
/usr/include/singular/singular/coeffs/rmodulo2m.h
/usr/include/singular/singular/coeffs/rmodulon.h
/usr/include/singular/singular/coeffs/shortfl.h
/usr/include/singular/singular/coeffs/si_gmp.h