They have a source iso to download, and it contains a license file with this at the top.
The Plan 9 software is provided under the terms of the Lucent Public License, Version 1.02, reproduced below, with the following notable exceptions: 1. No right is granted to create derivative works of or to redistribute (other than with the Plan 9 Operating System) the screen imprinter fonts identified in subdirectory /lib/font/bit/lucida and printer fonts (Lucida Sans Unicode, Lucida Sans Italic, Lucida Sans Demibold, Lucida Typewriter, Lucida Sans Typewriter83), identified in subdirectory /sys/lib/postscript/font. These directories contain material copyrights by B&H Inc. and Y&Y Inc. 2. The printer fonts identified in subdirectory /sys/lib/ghostscript/font are subject to the GNU GPL, reproduced in the file /LICENSE.gpl. 3. The ghostscript program in the subdirectory /sys/src/cmd/gs is covered by the Aladdin Free Public License, reproduced in the file /LICENSE.afpl.
There is a free software version of ghostscript, and if someone yanked out the font's, then it would be free. Plan9 people obviously don't want this, so I think the page should be delete, but I'll leave this until someone else has a chance to weigh in. --IanK (talk) 05:08, 29 October 2016 (EDT)
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the page “GNU Free Documentation License”.
The copyright and license notices on this page only apply to the text on this page. Any software or copyright-licenses or other similar notices described in this text has its own copyright notice and license, which can usually be found in the distribution or license text itself.