/usr/share/acl2-7.1/books/arithmetic-2/ is in acl2-books-source 7.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-7.1/books/arithmetic-2/floor-mod/
/usr/share/acl2-7.1/books/arithmetic-2/floor-mod/floor-mod-helper.lisp
/usr/share/acl2-7.1/books/arithmetic-2/floor-mod/floor-mod.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/
/usr/share/acl2-7.1/books/arithmetic-2/meta/cancel-terms-helper.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/cancel-terms-meta.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/collect-terms-meta.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/common-meta.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/expt-helper.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/expt.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/integerp-meta.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/integerp.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/mini-theories.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/non-linear.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/numerator-and-denominator.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/post.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/pre.lisp
/usr/share/acl2-7.1/books/arithmetic-2/meta/top.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/
/usr/share/acl2-7.1/books/arithmetic-2/pass1/basic-arithmetic-helper.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/basic-arithmetic.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/expt-helper.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/expt.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/inequalities.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/mini-theories.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/numerator-and-denominator-helper.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/numerator-and-denominator.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/prefer-times.lisp
/usr/share/acl2-7.1/books/arithmetic-2/pass1/top.lisp