“Since the normal tendency is to simplify, to trivialize, to eliminate the unfamiliar word or construction, the rule is praestat difficilior lectio. [. . .] When we choose the 'more difficult' reading, however, we must be sure that it is in itself a plausible reading. The principle should not be used in support of dubious syntax, or phrasing that it would not have been natural for the author to use. There is an important difference between a more difficult reading and a more unlikely reading.”