What's interesting about what you just stated is that the only reason current patents don't stifle innovation is that there is enough unpatented prior art that

What's interesting about what you just stated is that the only reason current patents don't stifle innovation is that there is enough unpatented prior art that someone can build a bridge. If someone did patent a simple bridge as stated above no one could build a truss bridge cause it would infringe. It would in effect stifle innovation. Patents only work when in old industries?