Let's say an algorithm is published and then afterwards it is implemented under GPLv3. Although the algorithm is mostly abstract, it does refer to specifications from a de facto standard in order to do its job.
Briefly, the stages are:
- Algorithm is published
- Implemented in GPLv3
Does implementing the algorithm under GPLv3 restrict its, i.e. the algorithm, re-implementation under permissive licenses? Are the latter derivative work if they are purely based on the original algo and not on whatever mods were added in step 2?