Flex carries the copyright used for BSD software, slightly modified
because it originated at the Lawrence Berkeley (not Livermore!) Laboratory,
which operates under a contract with the Department of Energy:

	Copyright (c) 1989 The Regents of the University of California.
	All rights reserved.

	This code is derived from software contributed to Berkeley by
	Vern Paxson.

	The United States Government has rights in this work pursuant to
	contract no. DE-AC03-76SF00098 between the United States Department of
	Energy and the University of California.

	Redistribution and use in source and binary forms are permitted
	provided that the above copyright notice and this paragraph are
	duplicated in all such forms and that any documentation,
	advertising materials, and other materials related to such
	distribution and use acknowledge that the software was developed
	by the University of California, Berkeley.  The name of the
	University may not be used to endorse or promote products derived
	from this software without specific prior written permission.
	THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
	IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
	WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

This basically says "do whatever you please with this software except
remove this notice".

Note that the "flex.skel" scanner skeleton carries no copyright notice.
You are free to do whatever you please with scanners generated using flex;
for them, you are not even bound by the above copyright.