/usr/share/acl2-6.3/books/ordinals/ is in acl2-books-source 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/ordinals/e0-ordinal.lisp
/usr/share/acl2-6.3/books/ordinals/lexicographic-book.lisp
/usr/share/acl2-6.3/books/ordinals/lexicographic-ordering-without-arithmetic.lisp
/usr/share/acl2-6.3/books/ordinals/lexicographic-ordering.lisp
/usr/share/acl2-6.3/books/ordinals/limits.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-addition.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-basic-thms.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-counter-examples.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-definitions.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-exponentiation.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-isomorphism.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-multiplication.lisp
/usr/share/acl2-6.3/books/ordinals/ordinal-total-order.lisp
/usr/share/acl2-6.3/books/ordinals/ordinals-without-arithmetic.lisp
/usr/share/acl2-6.3/books/ordinals/ordinals.lisp
/usr/share/acl2-6.3/books/ordinals/proof-of-well-foundedness.acl2
/usr/share/acl2-6.3/books/ordinals/proof-of-well-foundedness.lisp
/usr/share/acl2-6.3/books/ordinals/top-with-meta.lisp