> We very recently moved in the US from a first-to-invent to a first-to-file system. In the former, if you can provide evidence of the genesis of the invention

> We very recently moved in the US from a first-to-invent to a first-to-file system. In the former, if you can provide evidence of the genesis of the invention before the filing of the opponent's patent, then that may invalidate their patent. No, you would need to prove that your documented development of the invention predates the other party's documented development of the invention. Filing date does not matter in that case.