It is generally accepted that, even where a FOSS license is silent on patents, there is an implied patent license granted. The theory under US law is equitable estoppel, legal estoppel, or both. A license implied by equitable estoppel is one based on conduct, and a license implied by legal estoppel is based on the principle that one may not license a right, in the case of FOSS licenses the copyright, and then derogate from the right granted by asserting a different right.

The session will briefly cover the concepts of equitable estoppel and legal estoppel and argue that, while both trademarks and patents may be impliedly licensed by equitable estoppel, and patents are always licensed under a theory of legal estoppel, trademarks (qua trademark, not the pure letter string) will never be impliedly licensed under the doctrine of legal estoppel because enforcing trademark rights does not derogate from the copyright grant, i.e., the right to run, study, adapt, redistribute and improve the program.