/usr/share/acl2-6.3/books/concurrent-programs/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/concurrent-programs/bakery/
/usr/share/acl2-6.3/books/concurrent-programs/bakery/apply-total-order.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/fairenv.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/final-theorems.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/initial-state.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/inv-persists.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/inv-sufficient.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/labels.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/lexicographic-pos.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/lexicographic.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/measures.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/pos-temp.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/programs.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/properties-of-sets.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/properties.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/records.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/stutter1-match.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/stutter2.cert
/usr/share/acl2-6.3/books/concurrent-programs/bakery/variables.cert
/usr/share/acl2-6.3/books/concurrent-programs/german-protocol/
/usr/share/acl2-6.3/books/concurrent-programs/german-protocol/german.cert