/usr/ is in libalglib-dev 3.11.0-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/
/usr/include/libalglib/
/usr/include/libalglib/alglibinternal.h
/usr/include/libalglib/alglibmisc.h
/usr/include/libalglib/ap.h
/usr/include/libalglib/dataanalysis.h
/usr/include/libalglib/diffequations.h
/usr/include/libalglib/fasttransforms.h
/usr/include/libalglib/integration.h
/usr/include/libalglib/interpolation.h
/usr/include/libalglib/linalg.h
/usr/include/libalglib/optimization.h
/usr/include/libalglib/solvers.h
/usr/include/libalglib/specialfunctions.h
/usr/include/libalglib/statistics.h
/usr/include/libalglib/stdafx.h
/usr/lib/
/usr/lib/x86_64-linux-gnu/
/usr/lib/x86_64-linux-gnu/cmake/
/usr/lib/x86_64-linux-gnu/cmake/ALGLIB/
/usr/lib/x86_64-linux-gnu/cmake/ALGLIB/ALGLIBConfig.cmake
/usr/share/
/usr/share/doc/
/usr/share/doc/libalglib-dev/
/usr/share/doc/libalglib-dev/copyright
/usr/share/doc/libalglib-dev/manual.cpp.html
/usr/share/doc-base/
/usr/share/doc-base/alglib-cpp
/usr/lib/x86_64-linux-gnu/libalglib.so
/usr/share/doc/libalglib-dev/changelog.Debian.gz