Solution to Exc. 3.9
Lemma 3.3.2,3
fixed misnomers in solution of Exc. 3.9
Added Book_3_3_2,3
simplified 3.9, Import HoTTBook can be a problem
reverted to d7fa7f...
Lemmas 3.3.2 and 3.3.3 added
Backrefs for Lemmas 3.3.2 and 3.3.3 added
Solution to Exc. 3.9
Many improvements in the solution of Exc.3.9
all_to_empty_isequiv with hack
Many small fixes concerning Exc. 3.9
Merge pull request #543 from marcbezem/master

Lemmas 3.3.2 and 3.3.3 and Exc. 3.9