>
> I thought that to obtain or uphold a patent, one had only to prove that
> their idea was not common knowledge and was not in common usage at the
> time of the patent application. I didn't think that it mattered if there
> was prior artwork which was only known to a few people. If this were the
> case, most patents could be contested because most inventions are
> "re-invented" by several people and only one or a few ultimately decice to
> pursue it and get a patent.
>
Patents are only invented once and therefore any prior art forever precludes a
patent issue. The "reinvention" that you mention is really a combinatorial
patent (virtually all patents fall under this) that combines SOME of the
claims of multiple patents. If it performed all of the claims, it would be
infringing. A patent also has to fall into a statutory class and be useful.

Tom