Theorem isfin3-3

Description: Weakly Dedekind-infinite sets are exactly those with an _om -indexed descending chain of subsets. (Contributed by Stefan O'Rear, 7-Nov-2014)

	Ref	Expression
Assertion	isfin3-3	⊢ ( 𝐴 ∈ 𝑉 → ( 𝐴 ∈ FinIII ↔ ∀ 𝑓 ∈ ( 𝒫 𝐴 ↑m ω ) ( ∀ 𝑥 ∈ ω ( 𝑓 ‘ suc 𝑥 ) ⊆ ( 𝑓 ‘ 𝑥 ) → ∩ ran 𝑓 ∈ ran 𝑓 ) ) )

Proof

Step	Hyp	Ref	Expression
1		isf33lem	⊢ FinIII = { 𝑔 ∣ ∀ 𝑎 ∈ ( 𝒫 𝑔 ↑m ω ) ( ∀ 𝑏 ∈ ω ( 𝑎 ‘ suc 𝑏 ) ⊆ ( 𝑎 ‘ 𝑏 ) → ∩ ran 𝑎 ∈ ran 𝑎 ) }
2	1	isfin3ds	⊢ ( 𝐴 ∈ 𝑉 → ( 𝐴 ∈ FinIII ↔ ∀ 𝑓 ∈ ( 𝒫 𝐴 ↑m ω ) ( ∀ 𝑥 ∈ ω ( 𝑓 ‘ suc 𝑥 ) ⊆ ( 𝑓 ‘ 𝑥 ) → ∩ ran 𝑓 ∈ ran 𝑓 ) ) )