... the circle, are congruent. But the angles ACD and CAE, taken together,make a right angle, and the same is true of the two angles ABD and BAD. Hence, thetwo angles CAE and BAD are also congruent; ... congruence of anglesinscribed in the same segment of a circle, we have the congruence(2∗) ∠OBA≡ ∠OD C. Since, by hypothesis, CA and ACare parallel, we have(3∗) ∠OCA≡ ∠OAC,22according ... hold:7.8.9.10.11.12. a + (b + c) = (a + b) + c a + b = b + a a(bc) = (ab )c a( b + c) = ab + ac (a + b )c = ac + bcab = ba.8See also Schur, Math. Annalen, Vol. 55, p. 265.—Tr.28 and, consequently, that(6)...