Even though this material is available gratis there are some strings attached. You are free to use and modify this material as you see fit, however if you do modify it and then you redistribute it you are *required* to license the material under similar conditions. In other words, not only is this material free, it has to remain free forever. Meta-License ------------ You can chose to receive these materials under any *copyleft* license that meets the following two requirements: a) It permits freely copying and redistributing the material by any means and for whatever purpose, provided that the material is not modified. b) It permits the modification of material and distribution of the modified material by any means and for whatever purpose, provided that no further restrictions are imposed on the distribution or further modifications of the modified material. Examples of accepted/recommended Licenses are the GNU Free Documentation License, the Creative Commons Share Alike License, and the GNU General Public License. You are also allowed to receive this material under a *copyleft* license that imposes the sole further restriction that the modified material can not be used for military purposes, provided that the restriction applies to all military independently of allegiance.