/usr/include/ql/math/integrals/ is in libquantlib0-dev 1.7.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ql/math/integrals/all.hpp
/usr/include/ql/math/integrals/discreteintegrals.hpp
/usr/include/ql/math/integrals/filonintegral.hpp
/usr/include/ql/math/integrals/gaussianorthogonalpolynomial.hpp
/usr/include/ql/math/integrals/gaussianquadratures.hpp
/usr/include/ql/math/integrals/gausslobattointegral.hpp
/usr/include/ql/math/integrals/integral.hpp
/usr/include/ql/math/integrals/kronrodintegral.hpp
/usr/include/ql/math/integrals/segmentintegral.hpp
/usr/include/ql/math/integrals/simpsonintegral.hpp
/usr/include/ql/math/integrals/trapezoidintegral.hpp
/usr/include/ql/math/integrals/twodimensionalintegral.hpp