/usr/ is in libappindicator3-dev 12.10.1+18.04.20180322.1-0ubuntu1.
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..
/usr/include/
/usr/include/libappindicator3-0.1/
/usr/include/libappindicator3-0.1/libappindicator/
/usr/include/libappindicator3-0.1/libappindicator/app-indicator-enum-types.h
/usr/include/libappindicator3-0.1/libappindicator/app-indicator.h
/usr/lib/
/usr/lib/x86_64-linux-gnu/
/usr/lib/x86_64-linux-gnu/pkgconfig/
/usr/lib/x86_64-linux-gnu/pkgconfig/appindicator3-0.1.pc
/usr/share/
/usr/share/doc/
/usr/share/doc/libappindicator3-dev/
/usr/share/doc/libappindicator3-dev/copyright
/usr/share/gir-1.0/
/usr/share/gir-1.0/AppIndicator3-0.1.gir
/usr/share/vala/
/usr/share/vala/vapi/
/usr/share/vala/vapi/appindicator3-0.1.vapi
/usr/lib/x86_64-linux-gnu/libappindicator3.so
/usr/share/doc/libappindicator3-dev/changelog.Debian.gz