cite Hofmann and Streicher for univalence and categories (pointed out by Benedikt)
improved phrasing, more detail
Merge pull request #522 from mikeshulman/citehs

cite Hofmann and Streicher for univalence and categories
eliminate premature "Theorem", see #519
close #513
fix #514
parentheses in (k+1)-type
add exercise from Marc, close #498
marked errata for ga57eab2
mark errata for 39dfbd8
unmarked errata for a757864
unmarked errata for 4c4aee9
unmarked errata for 810aa94
Merge pull request #518 from sattlerc/master

removed an unnecessary restriction in exercise 7.5
Merge pull request #526 from mikeshulman/lem2.10.5ex

add exercise from Marc, close #498
Merge pull request #523 from mikeshulman/firsttime

eliminate premature "Theorem", see #519
marked errata for 810aa94
Merge pull request #525 from mikeshulman/lemma8.6.1

Lemma8.6.1
Merge pull request #524 from mikeshulman/lemma8.6.2

close #513
Typo in sec:equality-semigroups