some more exercises on W-types
added some index entries
one more exercise
oops, fix some typos
yet one more exercise
Uncommented the inclusion of main.labels
exercises on plump ordinals
Logical equivalence between torus and product of circles
refer to Taylor's book, clarify injectivity of i_Ord
6.4.2 isn't using funext, close #640
errata for ec1373a
remark 1+n=n+1 is not judgmental
clarify exercises 5.2 and 5.3, close #639
errata for bd29d77
close #638
errata for 43ea0a8
Insert missing 'e' on lhs invocation of W-elim.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Merge pull request #645 from ezyang/master

Insert missing 'e' on lhs invocation of W-elim.
errata for 0c6f0c8
Mark Errata (auto)