Proofs II, #1

 

derive C

1.	A ⊃ (B ≡ C)	premise
2.	~B v A	premise
3.	~(~B v C)	premise
4.	~~B & ~C	DEM	3
5.	~~B	simp	4
6.	A	d.s.	2, 5
7.	(B ≡ C)	m.p.	1,6
8.	(B ⊃ C) & (C ⊃ B)	BE	7
9.	(B ⊃ C)	simp	8
10.	B	DN	5
11.	C	mp	9,10