/usr/share/doc/libjs-mathjax-doc/html/upgrading/ is in libjs-mathjax-doc 2.7+20171212-1.
This file is owned by root:root, with mode 0o755.
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/usr/share/doc/libjs-mathjax-doc/html/upgrading/index.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/jsMath.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/upgrade.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-1.1.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.0.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.1.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.2.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.3.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.4.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.5.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.6.html
/usr/share/doc/libjs-mathjax-doc/html/upgrading/whats-new-2.7.html