some more exercises on W-types
one more exercise
oops, fix some typos
yet one more exercise
Merge branch 'master' into Wexercises
autoref -> cref
(marked) errata for e33ec32
another exercise specializing to bool
Merge pull request #629 from mikeshulman/Wexercises

Some more exercises on W-types
Merge pull request #689 from mikeshulman/errata

(marked) errata for e33ec32
Merge pull request #691 from mikeshulman/embeddings

another exercise, specializing the last one to bool