Read Chapter 4.
Deemphasize the non-obtuse-angle theorem (pp. 185-186) and "Note for
advanced students" (from p. 188 through the top of p. 190).
Also, we will not have time to study the proofs in this chapter as thoroughly
as those in Chapter 3; however, the **statements** of the propositions
(especially in the Saccheri-Lambert sections at the end) are very important
for understanding later chapters.

- ALPHA -- Prop. 4.3 (uniqueness) and 4.4 = Ex. 6
- BETA -- Prop. 4.5 = Ex. 8
- GAMMA -- Prop. 4.6 = Ex. 9
- DELTA -- Prop. 4.7 = Ex. 10
- EPSILON -- Prop. 4.8 = Ex. 11
- ZETA -- Prop 4.9 = Ex. 12
- ETA -- 4.10 = Ex. 13

- Exercise 4, p. 193
- Exercise 19, p. 197. What would happen if the plane is NOT semi-Euclidean? (See pp. 185-186.)
- Exercise 30, p. 199.
- Exercise 32, p. 199.

In addition, each *team* should turn in a single written version of
its proof.