/usr/share/acl2-6.3/books/cgen/ is in acl2-books 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/cgen/acl2s-parameter.o
/usr/share/acl2-6.3/books/cgen/base.o
/usr/share/acl2-6.3/books/cgen/basis.o
/usr/share/acl2-6.3/books/cgen/defdata.o
/usr/share/acl2-6.3/books/cgen/elim.o
/usr/share/acl2-6.3/books/cgen/graph-tc.o
/usr/share/acl2-6.3/books/cgen/library-support.o
/usr/share/acl2-6.3/books/cgen/main.o
/usr/share/acl2-6.3/books/cgen/mv-proof.o
/usr/share/acl2-6.3/books/cgen/num-list-fns.o
/usr/share/acl2-6.3/books/cgen/num-list-thms.o
/usr/share/acl2-6.3/books/cgen/random-state-basis1.o
/usr/share/acl2-6.3/books/cgen/random-state.o
/usr/share/acl2-6.3/books/cgen/random.o
/usr/share/acl2-6.3/books/cgen/rem-and-floor.o
/usr/share/acl2-6.3/books/cgen/simple-graph-array.o
/usr/share/acl2-6.3/books/cgen/splitnat.o
/usr/share/acl2-6.3/books/cgen/switchnat.o
/usr/share/acl2-6.3/books/cgen/top.o
/usr/share/acl2-6.3/books/cgen/type.o
/usr/share/acl2-6.3/books/cgen/utilities.o
/usr/share/acl2-6.3/books/cgen/with-timeout.o