/usr/share/acl2-6.3/books/textbook/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/textbook/chap10/
/usr/share/acl2-6.3/books/textbook/chap10/ac-example.cert
/usr/share/acl2-6.3/books/textbook/chap10/adder.cert
/usr/share/acl2-6.3/books/textbook/chap10/compiler.cert
/usr/share/acl2-6.3/books/textbook/chap10/fact.cert
/usr/share/acl2-6.3/books/textbook/chap10/insertion-sort.cert
/usr/share/acl2-6.3/books/textbook/chap10/tree.cert
/usr/share/acl2-6.3/books/textbook/chap11/
/usr/share/acl2-6.3/books/textbook/chap11/compress.cert
/usr/share/acl2-6.3/books/textbook/chap11/encap.cert
/usr/share/acl2-6.3/books/textbook/chap11/finite-sets.cert
/usr/share/acl2-6.3/books/textbook/chap11/how-many-soln1.cert
/usr/share/acl2-6.3/books/textbook/chap11/how-many-soln2.cert
/usr/share/acl2-6.3/books/textbook/chap11/mergesort.cert
/usr/share/acl2-6.3/books/textbook/chap11/perm-append.cert
/usr/share/acl2-6.3/books/textbook/chap11/perm.cert
/usr/share/acl2-6.3/books/textbook/chap11/qsort.cert
/usr/share/acl2-6.3/books/textbook/chap11/starters.cert
/usr/share/acl2-6.3/books/textbook/chap11/summations-book.cert
/usr/share/acl2-6.3/books/textbook/chap11/summations.cert
/usr/share/acl2-6.3/books/textbook/chap11/tautology.cert
/usr/share/acl2-6.3/books/textbook/chap11/xtr.cert
/usr/share/acl2-6.3/books/textbook/chap11/xtr2.cert
/usr/share/acl2-6.3/books/textbook/chap3/
/usr/share/acl2-6.3/books/textbook/chap3/programs.cert
/usr/share/acl2-6.3/books/textbook/chap4/
/usr/share/acl2-6.3/books/textbook/chap4/solutions-logic-mode.cert
/usr/share/acl2-6.3/books/textbook/chap4/solutions-program-mode.cert
/usr/share/acl2-6.3/books/textbook/chap5/
/usr/share/acl2-6.3/books/textbook/chap5/solutions.cert
/usr/share/acl2-6.3/books/textbook/chap6/
/usr/share/acl2-6.3/books/textbook/chap6/selected-solutions.cert