 Lewis argues that by this measure, worlds in which the mechanisms of nuclear warfare spontaneously fail will be less similar to the actual world than the post-nuclear apocalypse. That’s because the failure of those mechanisms will either lead to divergence from the actual world (if they fail partially) or widespread, diverse violations of law (if they fail completely). In the former case, there’s a violation of law that isn’t made up for in an increase in how much spatio-temporal match we get. In the latter case the gain we get in similarity is only an expansion of the spatio-temporal region throughout which perfect match of particular fact prevails, but that doesn’t help in getting us closer to actuality if we’ve added a big miracle. So in fact the nearest worlds are ones where a nuclear war occurs, and (3.5) is true.