exercise on qinv-univalence, close #553
spokes without a hub do work for truncations, close #515
unmarked errata for 2a7d913
Merge pull request #561 from mikeshulman/qinv-univalence

exercise on qinv-univalence, close #553
Merge pull request #562 from mikeshulman/spokes-no-hub

spokes without a hub do work for truncations, close #515
Mark Errata (auto)