If I can sidetrack this for a moment, could someone explain (or, far better, point me to a thorough analysis) the ramifications of if somebody were to "study" a

If I can sidetrack this for a moment, could someone explain (or, far better, point me to a thorough analysis) the ramifications of if somebody were to "study" a GPL-licensed program's source for its algorithms, formulas, etc., and then completely re-implement the package from scratch? I don't think I've seen this addressed in license FAQs. For a specific example, there is a book called _Calendrical Calculations_ which collects algorithms (and source, in Common Lisp, IIRC) for doing numerous time/date-related conversions. The authors patented the algorithms and the formulas as presented in the book. This seems a bit odd to me - it's not like they designed the Mayan calendar; while I respect that they did quite a bit of thorough research, that seems like the epitome of prior art. OTOH, the algorithms are also released under the GPL, in the form of the Emacs calendar mode. The book's license: (http://emr.cs.iit.edu/home/reingold/calendar-book/first-edition/calcode.shtml http://emr.cs.iit.edu/home/reingold/calendar-book/first-edit...) I'm a bit confused about the ramifications here - must one just ignore all of his research if you want to release date arithmetic code under a non-GPL free license? (I prefer the MIT/ISC and LGPL licenses) I thought the GPL only covered the implementation, but the apparent issue with the book's license really confuses me. I'm interested in writing a date arithmetic library in Lua or C, since having such a library specifically inside Emacs is of limited use, and my background is in history. In that specific case, the authors are probably willing to negotiate (and I may just be misunderstanding things) - I'm more interested in how that situation plays out in general.