Definition df-nninf 7007

Description: Define the set of nonincreasing sequences in 2_o ↑_𝑚 ω. Definition in Section 3.1 of [Pierik], p. 15. If we assumed excluded middle, this would be essentially the same as ℕ₀^* as defined at df-xnn0 9041 but in its absence the relationship between the two is more complicated. This definition would function much the same whether we used ω or ℕ₀, but the former allows us to take advantage of 2_o = {∅, 1_o} (df2o3 6327) so we adopt it. (Contributed by Jim Kingdon, 14-Jul-2022.)

Assertion

Ref	Expression
df-nninf	⊢ ℕ∞ = {𝑓 ∈ (2o ↑𝑚 ω) ∣ ∀𝑖 ∈ ω (𝑓‘suc 𝑖) ⊆ (𝑓‘𝑖)}

Distinct variable group:   𝑓,𝑖

Detailed syntax breakdown of Definition df-nninf

Step	Hyp	Ref	Expression
1		xnninf 7005	. 2 class ℕ∞
2		vi	. . . . . . . 8 setvar 𝑖
3	2	cv 1330	. . . . . . 7 class 𝑖
4	3	csuc 4287	. . . . . 6 class suc 𝑖
5		vf	. . . . . . 7 setvar 𝑓
6	5	cv 1330	. . . . . 6 class 𝑓
7	4, 6	cfv 5123	. . . . 5 class (𝑓‘suc 𝑖)
8	3, 6	cfv 5123	. . . . 5 class (𝑓‘𝑖)
9	7, 8	wss 3071	. . . 4 wff (𝑓‘suc 𝑖) ⊆ (𝑓‘𝑖)
10		com 4504	. . . 4 class ω
11	9, 2, 10	wral 2416	. . 3 wff ∀𝑖 ∈ ω (𝑓‘suc 𝑖) ⊆ (𝑓‘𝑖)
12		c2o 6307	. . . 4 class 2o
13		cmap 6542	. . . 4 class ↑𝑚
14	12, 10, 13	co 5774	. . 3 class (2o ↑𝑚 ω)
15	11, 5, 14	crab 2420	. 2 class {𝑓 ∈ (2o ↑𝑚 ω) ∣ ∀𝑖 ∈ ω (𝑓‘suc 𝑖) ⊆ (𝑓‘𝑖)}
16	1, 15	wceq 1331	1 wff ℕ∞ = {𝑓 ∈ (2o ↑𝑚 ω) ∣ ∀𝑖 ∈ ω (𝑓‘suc 𝑖) ⊆ (𝑓‘𝑖)}

This definition is referenced by:  infnninf  7022  nnnninf  7023  0nninf  13197  nninff  13198  nnsf  13199  peano4nninf  13200  nninfalllemn  13202  nninfalllem1  13203  nninfex  13205  nninfself  13209