/usr/include/dune/istl/ is in libdune-istl-dev 2.3.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/dune/istl/basearray.hh
/usr/include/dune/istl/bcrsmatrix.hh
/usr/include/dune/istl/bdmatrix.hh
/usr/include/dune/istl/btdmatrix.hh
/usr/include/dune/istl/bvector.hh
/usr/include/dune/istl/colcompmatrix.hh
/usr/include/dune/istl/diagonalmatrix.hh
/usr/include/dune/istl/gsetc.hh
/usr/include/dune/istl/ilu.hh
/usr/include/dune/istl/ilusubdomainsolver.hh
/usr/include/dune/istl/io.hh
/usr/include/dune/istl/istlexception.hh
/usr/include/dune/istl/matrix.hh
/usr/include/dune/istl/matrixindexset.hh
/usr/include/dune/istl/matrixmarket.hh
/usr/include/dune/istl/matrixmatrix.hh
/usr/include/dune/istl/matrixredistribute.hh
/usr/include/dune/istl/matrixutils.hh
/usr/include/dune/istl/multitypeblockmatrix.hh
/usr/include/dune/istl/multitypeblockvector.hh
/usr/include/dune/istl/novlpschwarz.hh
/usr/include/dune/istl/operators.hh
/usr/include/dune/istl/overlappingschwarz.hh
/usr/include/dune/istl/owneroverlapcopy.hh
/usr/include/dune/istl/paamg/
/usr/include/dune/istl/paamg/aggregates.hh
/usr/include/dune/istl/paamg/amg.hh
/usr/include/dune/istl/paamg/combinedfunctor.hh
/usr/include/dune/istl/paamg/construction.hh
/usr/include/dune/istl/paamg/dependency.hh
/usr/include/dune/istl/paamg/fastamg.hh
/usr/include/dune/istl/paamg/fastamgsmoother.hh
/usr/include/dune/istl/paamg/galerkin.hh
/usr/include/dune/istl/paamg/globalaggregates.hh
/usr/include/dune/istl/paamg/graph.hh
/usr/include/dune/istl/paamg/graphcreator.hh
/usr/include/dune/istl/paamg/hierarchy.hh
/usr/include/dune/istl/paamg/indicescoarsener.hh
/usr/include/dune/istl/paamg/kamg.hh
/usr/include/dune/istl/paamg/parameters.hh
/usr/include/dune/istl/paamg/pinfo.hh
/usr/include/dune/istl/paamg/properties.hh
/usr/include/dune/istl/paamg/renumberer.hh
/usr/include/dune/istl/paamg/smoother.hh
/usr/include/dune/istl/paamg/transfer.hh
/usr/include/dune/istl/paamg/twolevelmethod.hh
/usr/include/dune/istl/pardiso.hh
/usr/include/dune/istl/preconditioner.hh
/usr/include/dune/istl/preconditioners.hh
/usr/include/dune/istl/repartition.hh
/usr/include/dune/istl/scalarproducts.hh
/usr/include/dune/istl/scaledidmatrix.hh
/usr/include/dune/istl/schwarz.hh
/usr/include/dune/istl/solver.hh
/usr/include/dune/istl/solvercategory.hh
/usr/include/dune/istl/solvers.hh
/usr/include/dune/istl/solvertype.hh
/usr/include/dune/istl/superlu.hh
/usr/include/dune/istl/supermatrix.hh
/usr/include/dune/istl/umfpack.hh
/usr/include/dune/istl/vbvector.hh