The file "Trigonometry.tex" is released under the Knuthian Licence, the current CTAN entry for which reads along the following lines (amendments to grammar and spelling made in the following text) -- "This softÂware is copyÂright and you are exÂplicÂitly granted a liÂcence which allows you, the “user†of the softÂware, to copy, disÂtribute and/or modÂify the softÂware, provided only that if you modÂify and then re-distribute the softÂware it must be with a difÂferÂent name to that of the origÂiÂnal softÂware."