I'd like to open the floor, because many of us are coding away at a game engine someplace. What do you do, if you write a 2d physics library, and someone makes

I'd like to open the floor, because many of us are coding away at a game engine someplace. What do you do, if you write a 2d physics library, and someone makes a popular game. How do you retro-actively acquire the licensing? Prudent thing is I guess to take the time to get your IP in order before launch. But it's extra difficult for cash strapped solo indies ;)