/usr/share/tcltk/tcllib1.18/struct/ is in tcllib 1.18-dfsg-3.
This file is owned by root:root, with mode 0o755.
..
/usr/share/tcltk/tcllib1.18/struct/disjointset.tcl
/usr/share/tcltk/tcllib1.18/struct/graph.tcl
/usr/share/tcltk/tcllib1.18/struct/graph1.tcl
/usr/share/tcltk/tcllib1.18/struct/graph_c.tcl
/usr/share/tcltk/tcllib1.18/struct/graph_tcl.tcl
/usr/share/tcltk/tcllib1.18/struct/graphops.tcl
/usr/share/tcltk/tcllib1.18/struct/list.tcl
/usr/share/tcltk/tcllib1.18/struct/matrix.tcl
/usr/share/tcltk/tcllib1.18/struct/matrix1.tcl
/usr/share/tcltk/tcllib1.18/struct/pkgIndex.tcl
/usr/share/tcltk/tcllib1.18/struct/pool.tcl
/usr/share/tcltk/tcllib1.18/struct/prioqueue.tcl
/usr/share/tcltk/tcllib1.18/struct/queue.tcl
/usr/share/tcltk/tcllib1.18/struct/queue_c.tcl
/usr/share/tcltk/tcllib1.18/struct/queue_oo.tcl
/usr/share/tcltk/tcllib1.18/struct/queue_tcl.tcl
/usr/share/tcltk/tcllib1.18/struct/record.tcl
/usr/share/tcltk/tcllib1.18/struct/sets.tcl
/usr/share/tcltk/tcllib1.18/struct/sets_c.tcl
/usr/share/tcltk/tcllib1.18/struct/sets_tcl.tcl
/usr/share/tcltk/tcllib1.18/struct/skiplist.tcl
/usr/share/tcltk/tcllib1.18/struct/stack.tcl
/usr/share/tcltk/tcllib1.18/struct/stack_c.tcl
/usr/share/tcltk/tcllib1.18/struct/stack_oo.tcl
/usr/share/tcltk/tcllib1.18/struct/stack_tcl.tcl
/usr/share/tcltk/tcllib1.18/struct/struct.tcl
/usr/share/tcltk/tcllib1.18/struct/struct1.tcl
/usr/share/tcltk/tcllib1.18/struct/tree.tcl
/usr/share/tcltk/tcllib1.18/struct/tree1.tcl
/usr/share/tcltk/tcllib1.18/struct/tree_c.tcl
/usr/share/tcltk/tcllib1.18/struct/tree_tcl.tcl