tango-icon-theme is licensed under CC-BY-SA 2.5 which is non-DFSG free,
but is ubuntu-free. I think RMS is on record as not being a supporter of
CC.
** Changed in: tango-icon-theme (Ubuntu)
Status: Unconfirmed => Rejected
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vrms doesn't like to tango
https://launchpad.net/bugs/92614