Metamath Proof Explorer


Theorem axdc3

Description: Dependent Choice. Axiom DC1 of Schechter p. 149, with the addition of an initial value C . This theorem is weaker than the Axiom of Choice but is stronger than Countable Choice. It shows the existence of a sequence whose values can only be shown to exist (but cannot be constructed explicitly) and also depend on earlier values in the sequence. (Contributed by Mario Carneiro, 27-Jan-2013)

Ref Expression
Hypothesis axdc3.1 A V
Assertion axdc3 C A F : A 𝒫 A g g : ω A g = C k ω g suc k F g k

Proof

Step Hyp Ref Expression
1 axdc3.1 A V
2 feq1 t = s t : suc n A s : suc n A
3 fveq1 t = s t = s
4 3 eqeq1d t = s t = C s = C
5 fveq1 t = s t suc j = s suc j
6 fveq1 t = s t j = s j
7 6 fveq2d t = s F t j = F s j
8 5 7 eleq12d t = s t suc j F t j s suc j F s j
9 8 ralbidv t = s j n t suc j F t j j n s suc j F s j
10 suceq j = k suc j = suc k
11 10 fveq2d j = k s suc j = s suc k
12 2fveq3 j = k F s j = F s k
13 11 12 eleq12d j = k s suc j F s j s suc k F s k
14 13 cbvralvw j n s suc j F s j k n s suc k F s k
15 9 14 bitrdi t = s j n t suc j F t j k n s suc k F s k
16 2 4 15 3anbi123d t = s t : suc n A t = C j n t suc j F t j s : suc n A s = C k n s suc k F s k
17 16 rexbidv t = s n ω t : suc n A t = C j n t suc j F t j n ω s : suc n A s = C k n s suc k F s k
18 17 cbvabv t | n ω t : suc n A t = C j n t suc j F t j = s | n ω s : suc n A s = C k n s suc k F s k
19 eqid x t | n ω t : suc n A t = C j n t suc j F t j y t | n ω t : suc n A t = C j n t suc j F t j | dom y = suc dom x y dom x = x = x t | n ω t : suc n A t = C j n t suc j F t j y t | n ω t : suc n A t = C j n t suc j F t j | dom y = suc dom x y dom x = x
20 1 18 19 axdc3lem4 C A F : A 𝒫 A g g : ω A g = C k ω g suc k F g k