  The examples used above involve complex terms, disguised definite descriptions. But the same issues come up elsewhere as well, often in ways that are harder to deal with formally. Proper names constitute one well-known area of difficulties. The name “Cicero” and the name “Tully” denote the same person, so “Cicero is Tully” is true. Proper names are generally considered to be rigid, once a designation has been specified it does not change. This, in effect, makes “Cicero is Tully” into a necessary truth. How, then, could someone not know it? “Superman is Clark Kent” is even more difficult to deal with, since there is no actual person the names refer to. Thus while the sentence is true, not only might one not know it, but one might perfectly well believe Clark Kent exists, that is “Clark Kent” designates something, while not believing Superman exists. Existence issues are intertwined, in complex ways, with intensional matters. Further, the problems just sketched at the ground level continue up the type hierarchy. The property of being an equilateral triangle is coextensive with the property of being an equiangular triangle, though clearly meanings differ. Then one might say, “it is trivial that an equilateral triangle is an equilateral triangle,” yet one might deny that “it is trivial that an equilateral triangle is an equiangular triangle”.