Plan 9 license

[Richard Stallman]

You're right that the definition of free software, like the definition
of open source, need to be interpreted by people who are committed to
the goals with which those definitions were written.  Neither one is
designed to be fiendproof when interpreted by people that don't share
the goal.

	    You should also have the freedom to make modifications and use them
	    privately in your own work or play, without even mentioning that
	    they exist.

    The use of "should" rather than "must" causes it to appear that this is
    optional, but strongly encouraged.  This freedom would fall under 

I meant this to be a requirement.  I guess I should clarify the wording.