Ah, our first setback

After Safiya read through "Umbra et Umbra," she was confused. Like, "what did I just read" confused. On second glance, I can see why -- there's plenty of gaps in both the logic and the explanations. There are plenty of things I can backfill to make sense, and if I ever revisit the idea, I will -- but I'd rather spend my time during this challenge writing new settings, rather than rewriting older ones. If I get a spare moment, I'll add a badly needed simplified version.