fix statement of ex 4.2
unmarked errata for a9c974c
solution to ex 4.2
correct references in ex 4.2 solution
Merge pull request #496 from mikeshulman/ex4.2

Fix exercise 4.2, close #495
transport^A in 2.11.4 should be transport^B
unmarked errata for 2595167, close #501
fix a misuse of \refl
Some y's in lemma 7.5.14 should be f(x)'s.
unmarked errata for 00469d9
missing inl and inr after 2.12.5, close #499
unmarked errata for 7947494
remove spurious "on"
Merge pull request #505 from byorgey/master

remove spurious "on"
Merge pull request #502 from mikeshulman/thm2.11.4

Thm2.11.4
Merge pull request #503 from mikeshulman/lemma7.5.14

Lemma7.5.14
Merge pull request #504 from mikeshulman/thm2.12.5

Thm2.12.5
mark the last few errata
remove spurious function arguments
unmarked errata for 39dfbd8