“Knowledge, therefore, is like property. It must be published, declared, or in some other way so displayed that others cannot but take account of it. It must stand in their way. It must be emblematic, pointing backward at its possessor’s competitive skill. So close are knowledge and property that they are often thought to be continuous. Those who are entitled to knowledge feel they should be granted property as well, and those who are entitled to property believe a certain knowledge goes with it.”