/usr/include/polymake/internal/ is in libpolymake-dev-common 3.2r2-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/polymake/internal/AVL.h
/usr/include/polymake/internal/Array.h
/usr/include/polymake/internal/CharBuffer.h
/usr/include/polymake/internal/CombArray.h
/usr/include/polymake/internal/Incidence_and_SparseMatrix.h
/usr/include/polymake/internal/IndexDispenser.h
/usr/include/polymake/internal/PlainParser.h
/usr/include/polymake/internal/Wary.h
/usr/include/polymake/internal/alias.h
/usr/include/polymake/internal/assoc.h
/usr/include/polymake/internal/chunk_allocator.h
/usr/include/polymake/internal/comparators.h
/usr/include/polymake/internal/comparators_basic_defs.h
/usr/include/polymake/internal/comparators_ops.h
/usr/include/polymake/internal/constant_containers.h
/usr/include/polymake/internal/converters.h
/usr/include/polymake/internal/converters_basic_defs.h
/usr/include/polymake/internal/dense_linalg.h
/usr/include/polymake/internal/extend_algo.h
/usr/include/polymake/internal/hash_iterators.h
/usr/include/polymake/internal/iterator_zipper.h
/usr/include/polymake/internal/iterators.h
/usr/include/polymake/internal/linalg_exceptions.h
/usr/include/polymake/internal/matrix_methods.h
/usr/include/polymake/internal/matrix_rows_cols.h
/usr/include/polymake/internal/modified_containers.h
/usr/include/polymake/internal/nothing.h
/usr/include/polymake/internal/operations.h
/usr/include/polymake/internal/operations_basic_defs.h
/usr/include/polymake/internal/pool_allocator.h
/usr/include/polymake/internal/shared_object.h
/usr/include/polymake/internal/sparse.h
/usr/include/polymake/internal/sparse2d.h
/usr/include/polymake/internal/sparse2d_ruler.h
/usr/include/polymake/internal/sparse_linalg.h
/usr/include/polymake/internal/tree_containers.h
/usr/include/polymake/internal/tree_iterators.h
/usr/include/polymake/internal/type_manip.h
/usr/include/polymake/internal/type_union.h