填空题.When an invention is made, the inventor has three possible courses of action opening to him: he can give the invention to the 21 world by publishing it, keep the idea secret, or patent it. A granted patent is the result of a bargain strike between an inventor 22 and the state, by which the inventor gets a limited period of monopoly and publishes full details of his invention to the public after that period terminates. Only in the most exceptional circumstances the 23 lifespan of a patent extended to alter this normal process of events. Because a patent remains temporarily public after it has terminated, 24 the shelves of the library attached to the patent office contain details of literal millions of ideas that are free for anyone to use and, if older 25 than half a century, sometimes even patent. Indeed, patent experts often 26 advise anyone wishing to avoid the high cost of conducting a search through lively patents that the one sure way of avoiding violation of 27 any other inventor's right is to plagiarize a dead patent. However, 28 because publication of an idea in any other form permanently validates further patents on that idea, it is traditionally safe to take ideas from other areas of print. Much modern technological advance is based on these presumptions of legal security. Anyone closely involved in patents and inventions soon learns that most "new" ideas are, in fact, as very old as the hills. It is their reduction to 29 commercial practice, either through necessity, or dedication, or through the availability of new technology, makes news and money. 30