P. 104 of Theorem List - Metamath Proof Explorer

Theorem List for Metamath Proof Explorer - 10301-10400   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	fin23lem36 10301*	Lemma for fin23 10342. Weak order property of 𝑌. (Contributed by Stefan O'Rear, 2-Nov-2014.)
⊢ 𝐹 = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}    &   ⊢ (𝜑 → ℎ:ω–1-1→V)    &   ⊢ (𝜑 → ∪ ran ℎ ⊆ 𝐺)    &   ⊢ (𝜑 → ∀𝑗((𝑗:ω–1-1→V ∧ ∪ ran 𝑗 ⊆ 𝐺) → ((𝑖‘𝑗):ω–1-1→V ∧ ∪ ran (𝑖‘𝑗) ⊊ ∪ ran 𝑗)))    &   ⊢ 𝑌 = (rec(𝑖, ℎ) ↾ ω)    ⇒   ⊢ (((𝐴 ∈ ω ∧ 𝐵 ∈ ω) ∧ (𝐵 ⊆ 𝐴 ∧ 𝜑)) → ∪ ran (𝑌‘𝐴) ⊆ ∪ ran (𝑌‘𝐵))
Theorem	fin23lem38 10302*	Lemma for fin23 10342. The contradictory chain has no minimum. (Contributed by Stefan O'Rear, 2-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}    &   ⊢ (𝜑 → ℎ:ω–1-1→V)    &   ⊢ (𝜑 → ∪ ran ℎ ⊆ 𝐺)    &   ⊢ (𝜑 → ∀𝑗((𝑗:ω–1-1→V ∧ ∪ ran 𝑗 ⊆ 𝐺) → ((𝑖‘𝑗):ω–1-1→V ∧ ∪ ran (𝑖‘𝑗) ⊊ ∪ ran 𝑗)))    &   ⊢ 𝑌 = (rec(𝑖, ℎ) ↾ ω)    ⇒   ⊢ (𝜑 → ¬ ∩ ran (𝑏 ∈ ω ↦ ∪ ran (𝑌‘𝑏)) ∈ ran (𝑏 ∈ ω ↦ ∪ ran (𝑌‘𝑏)))
Theorem	fin23lem39 10303*	Lemma for fin23 10342. Thus, we have that 𝑔 could not have been in 𝐹 after all. (Contributed by Stefan O'Rear, 4-Nov-2014.)
⊢ 𝐹 = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}    &   ⊢ (𝜑 → ℎ:ω–1-1→V)    &   ⊢ (𝜑 → ∪ ran ℎ ⊆ 𝐺)    &   ⊢ (𝜑 → ∀𝑗((𝑗:ω–1-1→V ∧ ∪ ran 𝑗 ⊆ 𝐺) → ((𝑖‘𝑗):ω–1-1→V ∧ ∪ ran (𝑖‘𝑗) ⊊ ∪ ran 𝑗)))    &   ⊢ 𝑌 = (rec(𝑖, ℎ) ↾ ω)    ⇒   ⊢ (𝜑 → ¬ 𝐺 ∈ 𝐹)
Theorem	fin23lem40 10304*	Lemma for fin23 10342. FinII sets satisfy the descending chain condition. (Contributed by Stefan O'Rear, 3-Nov-2014.)
⊢ 𝐹 = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}    ⇒   ⊢ (𝐴 ∈ FinII → 𝐴 ∈ 𝐹)
Theorem	fin23lem41 10305*	Lemma for fin23 10342. A set which satisfies the descending sequence condition must be III-finite. (Contributed by Stefan O'Rear, 2-Nov-2014.)
⊢ 𝐹 = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}    ⇒   ⊢ (𝐴 ∈ 𝐹 → 𝐴 ∈ FinIII)
Theorem	isf32lem1 10306*	Lemma for isfin3-2 10320. Derive weak ordering property. (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    ⇒   ⊢ (((𝐴 ∈ ω ∧ 𝐵 ∈ ω) ∧ (𝐵 ⊆ 𝐴 ∧ 𝜑)) → (𝐹‘𝐴) ⊆ (𝐹‘𝐵))
Theorem	isf32lem2 10307*	Lemma for isfin3-2 10320. Non-minimum implies that there is always another decrease. (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    ⇒   ⊢ ((𝜑 ∧ 𝐴 ∈ ω) → ∃𝑎 ∈ ω (𝐴 ∈ 𝑎 ∧ (𝐹‘suc 𝑎) ⊊ (𝐹‘𝑎)))
Theorem	isf32lem3 10308*	Lemma for isfin3-2 10320. Being a chain, difference sets are disjoint (one case). (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    ⇒   ⊢ (((𝐴 ∈ ω ∧ 𝐵 ∈ ω) ∧ (𝐵 ∈ 𝐴 ∧ 𝜑)) → (((𝐹‘𝐴) ∖ (𝐹‘suc 𝐴)) ∩ ((𝐹‘𝐵) ∖ (𝐹‘suc 𝐵))) = ∅)
Theorem	isf32lem4 10309*	Lemma for isfin3-2 10320. Being a chain, difference sets are disjoint. (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    ⇒   ⊢ (((𝜑 ∧ 𝐴 ≠ 𝐵) ∧ (𝐴 ∈ ω ∧ 𝐵 ∈ ω)) → (((𝐹‘𝐴) ∖ (𝐹‘suc 𝐴)) ∩ ((𝐹‘𝐵) ∖ (𝐹‘suc 𝐵))) = ∅)
Theorem	isf32lem5 10310*	Lemma for isfin3-2 10320. There are infinite decrease points. (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    &   ⊢ 𝑆 = {𝑦 ∈ ω ∣ (𝐹‘suc 𝑦) ⊊ (𝐹‘𝑦)}    ⇒   ⊢ (𝜑 → ¬ 𝑆 ∈ Fin)
Theorem	isf32lem6 10311*	Lemma for isfin3-2 10320. Each K value is nonempty. (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    &   ⊢ 𝑆 = {𝑦 ∈ ω ∣ (𝐹‘suc 𝑦) ⊊ (𝐹‘𝑦)}    &   ⊢ 𝐽 = (𝑢 ∈ ω ↦ (℩𝑣 ∈ 𝑆 (𝑣 ∩ 𝑆) ≈ 𝑢))    &   ⊢ 𝐾 = ((𝑤 ∈ 𝑆 ↦ ((𝐹‘𝑤) ∖ (𝐹‘suc 𝑤))) ∘ 𝐽)    ⇒   ⊢ ((𝜑 ∧ 𝐴 ∈ ω) → (𝐾‘𝐴) ≠ ∅)
Theorem	isf32lem7 10312*	Lemma for isfin3-2 10320. Different K values are disjoint. (Contributed by Stefan O'Rear, 5-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    &   ⊢ 𝑆 = {𝑦 ∈ ω ∣ (𝐹‘suc 𝑦) ⊊ (𝐹‘𝑦)}    &   ⊢ 𝐽 = (𝑢 ∈ ω ↦ (℩𝑣 ∈ 𝑆 (𝑣 ∩ 𝑆) ≈ 𝑢))    &   ⊢ 𝐾 = ((𝑤 ∈ 𝑆 ↦ ((𝐹‘𝑤) ∖ (𝐹‘suc 𝑤))) ∘ 𝐽)    ⇒   ⊢ (((𝜑 ∧ 𝐴 ≠ 𝐵) ∧ (𝐴 ∈ ω ∧ 𝐵 ∈ ω)) → ((𝐾‘𝐴) ∩ (𝐾‘𝐵)) = ∅)
Theorem	isf32lem8 10313*	Lemma for isfin3-2 10320. K sets are subsets of the base. (Contributed by Stefan O'Rear, 6-Nov-2014.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    &   ⊢ 𝑆 = {𝑦 ∈ ω ∣ (𝐹‘suc 𝑦) ⊊ (𝐹‘𝑦)}    &   ⊢ 𝐽 = (𝑢 ∈ ω ↦ (℩𝑣 ∈ 𝑆 (𝑣 ∩ 𝑆) ≈ 𝑢))    &   ⊢ 𝐾 = ((𝑤 ∈ 𝑆 ↦ ((𝐹‘𝑤) ∖ (𝐹‘suc 𝑤))) ∘ 𝐽)    ⇒   ⊢ ((𝜑 ∧ 𝐴 ∈ ω) → (𝐾‘𝐴) ⊆ 𝐺)
Theorem	isf32lem9 10314*	Lemma for isfin3-2 10320. Construction of the onto function. (Contributed by Stefan O'Rear, 5-Nov-2014.) (Revised by Mario Carneiro, 2-Oct-2015.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    &   ⊢ 𝑆 = {𝑦 ∈ ω ∣ (𝐹‘suc 𝑦) ⊊ (𝐹‘𝑦)}    &   ⊢ 𝐽 = (𝑢 ∈ ω ↦ (℩𝑣 ∈ 𝑆 (𝑣 ∩ 𝑆) ≈ 𝑢))    &   ⊢ 𝐾 = ((𝑤 ∈ 𝑆 ↦ ((𝐹‘𝑤) ∖ (𝐹‘suc 𝑤))) ∘ 𝐽)    &   ⊢ 𝐿 = (𝑡 ∈ 𝐺 ↦ (℩𝑠(𝑠 ∈ ω ∧ 𝑡 ∈ (𝐾‘𝑠))))    ⇒   ⊢ (𝜑 → 𝐿:𝐺–onto→ω)
Theorem	isf32lem10 10315*	Lemma for isfin3-2 . Write in terms of weak dominance. (Contributed by Stefan O'Rear, 6-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝜑 → 𝐹:ω⟶𝒫 𝐺)    &   ⊢ (𝜑 → ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥))    &   ⊢ (𝜑 → ¬ ∩ ran 𝐹 ∈ ran 𝐹)    &   ⊢ 𝑆 = {𝑦 ∈ ω ∣ (𝐹‘suc 𝑦) ⊊ (𝐹‘𝑦)}    &   ⊢ 𝐽 = (𝑢 ∈ ω ↦ (℩𝑣 ∈ 𝑆 (𝑣 ∩ 𝑆) ≈ 𝑢))    &   ⊢ 𝐾 = ((𝑤 ∈ 𝑆 ↦ ((𝐹‘𝑤) ∖ (𝐹‘suc 𝑤))) ∘ 𝐽)    &   ⊢ 𝐿 = (𝑡 ∈ 𝐺 ↦ (℩𝑠(𝑠 ∈ ω ∧ 𝑡 ∈ (𝐾‘𝑠))))    ⇒   ⊢ (𝜑 → (𝐺 ∈ 𝑉 → ω ≼* 𝐺))
Theorem	isf32lem11 10316*	Lemma for isfin3-2 10320. Remove hypotheses from isf32lem10 10315. (Contributed by Stefan O'Rear, 17-May-2015.)
⊢ ((𝐺 ∈ 𝑉 ∧ (𝐹:ω⟶𝒫 𝐺 ∧ ∀𝑏 ∈ ω (𝐹‘suc 𝑏) ⊆ (𝐹‘𝑏) ∧ ¬ ∩ ran 𝐹 ∈ ran 𝐹)) → ω ≼* 𝐺)
Theorem	isf32lem12 10317*	Lemma for isfin3-2 10320. (Contributed by Stefan O'Rear, 6-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}    ⇒   ⊢ (𝐺 ∈ 𝑉 → (¬ ω ≼* 𝐺 → 𝐺 ∈ 𝐹))
Theorem	isfin32i 10318	One half of isfin3-2 10320. (Contributed by Mario Carneiro, 3-Jun-2015.)
⊢ (𝐴 ∈ FinIII → ¬ ω ≼* 𝐴)
Theorem	isf33lem 10319*	Lemma for isfin3-3 10321. (Contributed by Stefan O'Rear, 17-May-2015.)
⊢ FinIII = {𝑔 ∣ ∀𝑎 ∈ (𝒫 𝑔 ↑m ω)(∀𝑥 ∈ ω (𝑎‘suc 𝑥) ⊆ (𝑎‘𝑥) → ∩ ran 𝑎 ∈ ran 𝑎)}
Theorem	isfin3-2 10320	Weakly Dedekind-infinite sets are exactly those which can be mapped onto ω. (Contributed by Stefan O'Rear, 6-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ FinIII ↔ ¬ ω ≼* 𝐴))
Theorem	isfin3-3 10321*	Weakly Dedekind-infinite sets are exactly those with an ω-indexed descending chain of subsets. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ FinIII ↔ ∀𝑓 ∈ (𝒫 𝐴 ↑m ω)(∀𝑥 ∈ ω (𝑓‘suc 𝑥) ⊆ (𝑓‘𝑥) → ∩ ran 𝑓 ∈ ran 𝑓)))
Theorem	fin33i 10322*	Inference from isfin3-3 10321. (This is actually a bit stronger than isfin3-3 10321 because it does not assume 𝐹 is a set and does not use the Axiom of Infinity either.) (Contributed by Mario Carneiro, 17-May-2015.)
⊢ ((𝐴 ∈ FinIII ∧ 𝐹:ω⟶𝒫 𝐴 ∧ ∀𝑥 ∈ ω (𝐹‘suc 𝑥) ⊆ (𝐹‘𝑥)) → ∩ ran 𝐹 ∈ ran 𝐹)
Theorem	compsscnvlem 10323*	Lemma for compsscnv 10324. (Contributed by Mario Carneiro, 17-May-2015.)
⊢ ((𝑥 ∈ 𝒫 𝐴 ∧ 𝑦 = (𝐴 ∖ 𝑥)) → (𝑦 ∈ 𝒫 𝐴 ∧ 𝑥 = (𝐴 ∖ 𝑦)))
Theorem	compsscnv 10324*	Complementation on a power set lattice is an involution. (Contributed by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ ◡𝐹 = 𝐹
Theorem	isf34lem1 10325*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ ((𝐴 ∈ 𝑉 ∧ 𝑋 ⊆ 𝐴) → (𝐹‘𝑋) = (𝐴 ∖ 𝑋))
Theorem	isf34lem2 10326*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ (𝐴 ∈ 𝑉 → 𝐹:𝒫 𝐴⟶𝒫 𝐴)
Theorem	compssiso 10327*	Complementation is an antiautomorphism on power set lattices. (Contributed by Stefan O'Rear, 4-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ (𝐴 ∈ 𝑉 → 𝐹 Isom [⊊] , ◡ [⊊] (𝒫 𝐴, 𝒫 𝐴))
Theorem	isf34lem3 10328*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ ((𝐴 ∈ 𝑉 ∧ 𝑋 ⊆ 𝒫 𝐴) → (𝐹 “ (𝐹 “ 𝑋)) = 𝑋)
Theorem	compss 10329*	Express image under of the complementation isomorphism. (Contributed by Stefan O'Rear, 5-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ (𝐹 “ 𝐺) = {𝑦 ∈ 𝒫 𝐴 ∣ (𝐴 ∖ 𝑦) ∈ 𝐺}
Theorem	isf34lem4 10330*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ ((𝐴 ∈ 𝑉 ∧ (𝑋 ⊆ 𝒫 𝐴 ∧ 𝑋 ≠ ∅)) → (𝐹‘∪ 𝑋) = ∩ (𝐹 “ 𝑋))
Theorem	isf34lem5 10331*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ ((𝐴 ∈ 𝑉 ∧ (𝑋 ⊆ 𝒫 𝐴 ∧ 𝑋 ≠ ∅)) → (𝐹‘∩ 𝑋) = ∪ (𝐹 “ 𝑋))
Theorem	isf34lem7 10332*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ ((𝐴 ∈ FinIII ∧ 𝐺:ω⟶𝒫 𝐴 ∧ ∀𝑦 ∈ ω (𝐺‘𝑦) ⊆ (𝐺‘suc 𝑦)) → ∪ ran 𝐺 ∈ ran 𝐺)
Theorem	isf34lem6 10333*	Lemma for isfin3-4 10335. (Contributed by Stefan O'Rear, 7-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ 𝐹 = (𝑥 ∈ 𝒫 𝐴 ↦ (𝐴 ∖ 𝑥))    ⇒   ⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ FinIII ↔ ∀𝑓 ∈ (𝒫 𝐴 ↑m ω)(∀𝑦 ∈ ω (𝑓‘𝑦) ⊆ (𝑓‘suc 𝑦) → ∪ ran 𝑓 ∈ ran 𝑓)))
Theorem	fin34i 10334*	Inference from isfin3-4 10335. (Contributed by Mario Carneiro, 17-May-2015.)
⊢ ((𝐴 ∈ FinIII ∧ 𝐺:ω⟶𝒫 𝐴 ∧ ∀𝑥 ∈ ω (𝐺‘𝑥) ⊆ (𝐺‘suc 𝑥)) → ∪ ran 𝐺 ∈ ran 𝐺)
Theorem	isfin3-4 10335*	Weakly Dedekind-infinite sets are exactly those with an ω-indexed ascending chain of subsets. (Contributed by Stefan O'Rear, 7-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ FinIII ↔ ∀𝑓 ∈ (𝒫 𝐴 ↑m ω)(∀𝑥 ∈ ω (𝑓‘𝑥) ⊆ (𝑓‘suc 𝑥) → ∪ ran 𝑓 ∈ ran 𝑓)))
Theorem	fin11a 10336	Every I-finite set is Ia-finite. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ Fin → 𝐴 ∈ FinIa)
Theorem	enfin1ai 10337	Ia-finiteness is a cardinal property. (Contributed by Mario Carneiro, 18-May-2015.)
⊢ (𝐴 ≈ 𝐵 → (𝐴 ∈ FinIa → 𝐵 ∈ FinIa))
Theorem	isfin1-2 10338	A set is finite in the usual sense iff the power set of its power set is Dedekind finite. (Contributed by Stefan O'Rear, 3-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ Fin ↔ 𝒫 𝒫 𝐴 ∈ FinIV)
Theorem	isfin1-3 10339	A set is I-finite iff every system of subsets contains a maximal subset. Definition I of [Levy58] p. 2. (Contributed by Stefan O'Rear, 4-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ Fin ↔ ◡ [⊊] Fr 𝒫 𝐴))
Theorem	isfin1-4 10340	A set is I-finite iff every system of subsets contains a minimal subset. (Contributed by Stefan O'Rear, 4-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ Fin ↔ [⊊] Fr 𝒫 𝐴))
Theorem	dffin1-5 10341	Compact quantifier-free version of the standard definition df-fin 8922. (Contributed by Stefan O'Rear, 6-Jan-2015.)
⊢ Fin = ( ≈ “ ω)
Theorem	fin23 10342	Every II-finite set (every chain of subsets has a maximal element) is III-finite (has no denumerable collection of subsets). The proof here is the only one I could find, from http://matwbn.icm.edu.pl/ksiazki/fm/fm6/fm619.pdf p.94 (writeup by Tarski, credited to Kuratowski). Translated into English and modern notation, the proof proceeds as follows (variables renamed for uniqueness): Suppose for a contradiction that 𝐴 is a set which is II-finite but not III-finite. For any countable sequence of distinct subsets 𝑇 of 𝐴, we can form a decreasing sequence of nonempty subsets (𝑈‘𝑇) by taking finite intersections of initial segments of 𝑇 while skipping over any element of 𝑇 which would cause the intersection to be empty. By II-finiteness (as fin2i2 10271) this sequence contains its intersection, call it 𝑌; since by induction every subset in the sequence 𝑈 is nonempty, the intersection must be nonempty. Suppose that an element 𝑋 of 𝑇 has nonempty intersection with 𝑌. Thus, said element has a nonempty intersection with the corresponding element of 𝑈, therefore it was used in the construction of 𝑈 and all further elements of 𝑈 are subsets of 𝑋, thus 𝑋 contains the 𝑌. That is, all elements of 𝑋 either contain 𝑌 or are disjoint from it. Since there are only two cases, there must exist an infinite subset of 𝑇 which uniformly either contain 𝑌 or are disjoint from it. In the former case we can create an infinite set by subtracting 𝑌 from each element. In either case, call the result 𝑍; this is an infinite set of subsets of 𝐴, each of which is disjoint from 𝑌 and contained in the union of 𝑇; the union of 𝑍 is strictly contained in the union of 𝑇, because only the latter is a superset of the nonempty set 𝑌. The preceding four steps may be iterated a countable number of times starting from the assumed denumerable set of subsets to produce a denumerable sequence 𝐵 of the 𝑇 sets from each stage. Great caution is required to avoid ax-dc 10399 here; in particular an effective version of the pigeonhole principle (for aleph-null pigeons and 2 holes) is required. Since a denumerable set of subsets is assumed to exist, we can conclude ω ∈ V without the axiom. This 𝐵 sequence is strictly decreasing, thus it has no minimum, contradicting the first assumption. (Contributed by Stefan O'Rear, 2-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ FinII → 𝐴 ∈ FinIII)
Theorem	fin34 10343	Every III-finite set is IV-finite. (Contributed by Stefan O'Rear, 30-Oct-2014.)
⊢ (𝐴 ∈ FinIII → 𝐴 ∈ FinIV)
Theorem	isfin5-2 10344	Alternate definition of V-finite which emphasizes the idempotent behavior of V-infinite sets. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ FinV ↔ ¬ (𝐴 ≠ ∅ ∧ 𝐴 ≈ (𝐴 ⊔ 𝐴))))
Theorem	fin45 10345	Every IV-finite set is V-finite: if we can pack two copies of the set into itself, we can certainly leave space. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Proof shortened by Mario Carneiro, 18-May-2015.)
⊢ (𝐴 ∈ FinIV → 𝐴 ∈ FinV)
Theorem	fin56 10346	Every V-finite set is VI-finite because multiplication dominates addition for cardinals. (Contributed by Stefan O'Rear, 29-Oct-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ FinV → 𝐴 ∈ FinVI)
Theorem	fin17 10347	Every I-finite set is VII-finite. (Contributed by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ Fin → 𝐴 ∈ FinVII)
Theorem	fin67 10348	Every VI-finite set is VII-finite. (Contributed by Stefan O'Rear, 29-Oct-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ FinVI → 𝐴 ∈ FinVII)
Theorem	isfin7-2 10349	A set is VII-finite iff it is non-well-orderable or finite. (Contributed by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ 𝑉 → (𝐴 ∈ FinVII ↔ (𝐴 ∈ dom card → 𝐴 ∈ Fin)))
Theorem	fin71num 10350	A well-orderable set is VII-finite iff it is I-finite. Thus, even without choice, on the class of well-orderable sets all eight definitions of finite set coincide. (Contributed by Mario Carneiro, 18-May-2015.)
⊢ (𝐴 ∈ dom card → (𝐴 ∈ FinVII ↔ 𝐴 ∈ Fin))
Theorem	dffin7-2 10351	Class form of isfin7-2 10349. (Contributed by Mario Carneiro, 17-May-2015.)
⊢ FinVII = (Fin ∪ (V ∖ dom card))
Theorem	dfacfin7 10352	Axiom of Choice equivalent: the VII-finite sets are the same as I-finite sets. (Contributed by Mario Carneiro, 18-May-2015.)
⊢ (CHOICE ↔ FinVII = Fin)
Theorem	fin1a2lem1 10353	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝑆 = (𝑥 ∈ On ↦ suc 𝑥)    ⇒   ⊢ (𝐴 ∈ On → (𝑆‘𝐴) = suc 𝐴)
Theorem	fin1a2lem2 10354	Lemma for fin1a2 10368. The successor operation on the ordinal numbers is injective or one-to-one. Lemma 1.17 of [Schloeder] p. 2. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝑆 = (𝑥 ∈ On ↦ suc 𝑥)    ⇒   ⊢ 𝑆:On–1-1→On
Theorem	fin1a2lem3 10355	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐸 = (𝑥 ∈ ω ↦ (2o ·o 𝑥))    ⇒   ⊢ (𝐴 ∈ ω → (𝐸‘𝐴) = (2o ·o 𝐴))
Theorem	fin1a2lem4 10356	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐸 = (𝑥 ∈ ω ↦ (2o ·o 𝑥))    ⇒   ⊢ 𝐸:ω–1-1→ω
Theorem	fin1a2lem5 10357	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐸 = (𝑥 ∈ ω ↦ (2o ·o 𝑥))    ⇒   ⊢ (𝐴 ∈ ω → (𝐴 ∈ ran 𝐸 ↔ ¬ suc 𝐴 ∈ ran 𝐸))
Theorem	fin1a2lem6 10358	Lemma for fin1a2 10368. Establish that ω can be broken into two equipollent pieces. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐸 = (𝑥 ∈ ω ↦ (2o ·o 𝑥))    &   ⊢ 𝑆 = (𝑥 ∈ On ↦ suc 𝑥)    ⇒   ⊢ (𝑆 ↾ ran 𝐸):ran 𝐸–1-1-onto→(ω ∖ ran 𝐸)
Theorem	fin1a2lem7 10359*	Lemma for fin1a2 10368. Split a III-infinite set in two pieces. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ 𝐸 = (𝑥 ∈ ω ↦ (2o ·o 𝑥))    &   ⊢ 𝑆 = (𝑥 ∈ On ↦ suc 𝑥)    ⇒   ⊢ ((𝐴 ∈ 𝑉 ∧ ∀𝑦 ∈ 𝒫 𝐴(𝑦 ∈ FinIII ∨ (𝐴 ∖ 𝑦) ∈ FinIII)) → 𝐴 ∈ FinIII)
Theorem	fin1a2lem8 10360*	Lemma for fin1a2 10368. Split a III-infinite set in two pieces. (Contributed by Stefan O'Rear, 7-Nov-2014.)
⊢ ((𝐴 ∈ 𝑉 ∧ ∀𝑥 ∈ 𝒫 𝐴(𝑥 ∈ FinIII ∨ (𝐴 ∖ 𝑥) ∈ FinIII)) → 𝐴 ∈ FinIII)
Theorem	fin1a2lem9 10361*	Lemma for fin1a2 10368. In a chain of finite sets, initial segments are finite. (Contributed by Stefan O'Rear, 8-Nov-2014.)
⊢ (( [⊊] Or 𝑋 ∧ 𝑋 ⊆ Fin ∧ 𝐴 ∈ ω) → {𝑏 ∈ 𝑋 ∣ 𝑏 ≼ 𝐴} ∈ Fin)
Theorem	fin1a2lem10 10362	Lemma for fin1a2 10368. A nonempty finite union of members of a chain is a member of the chain. (Contributed by Stefan O'Rear, 8-Nov-2014.)
⊢ ((𝐴 ≠ ∅ ∧ 𝐴 ∈ Fin ∧ [⊊] Or 𝐴) → ∪ 𝐴 ∈ 𝐴)
Theorem	fin1a2lem11 10363*	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 8-Nov-2014.)
⊢ (( [⊊] Or 𝐴 ∧ 𝐴 ⊆ Fin) → ran (𝑏 ∈ ω ↦ ∪ {𝑐 ∈ 𝐴 ∣ 𝑐 ≼ 𝑏}) = (𝐴 ∪ {∅}))
Theorem	fin1a2lem12 10364	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 8-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (((𝐴 ⊆ 𝒫 𝐵 ∧ [⊊] Or 𝐴 ∧ ¬ ∪ 𝐴 ∈ 𝐴) ∧ (𝐴 ⊆ Fin ∧ 𝐴 ≠ ∅)) → ¬ 𝐵 ∈ FinIII)
Theorem	fin1a2lem13 10365	Lemma for fin1a2 10368. (Contributed by Stefan O'Rear, 8-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (((𝐴 ⊆ 𝒫 𝐵 ∧ [⊊] Or 𝐴 ∧ ¬ ∪ 𝐴 ∈ 𝐴) ∧ (¬ 𝐶 ∈ Fin ∧ 𝐶 ∈ 𝐴)) → ¬ (𝐵 ∖ 𝐶) ∈ FinII)
Theorem	fin12 10366	Weak theorem which skips Ia but has a trivial proof, needed to prove fin1a2 10368. (Contributed by Stefan O'Rear, 8-Nov-2014.) (Revised by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ Fin → 𝐴 ∈ FinII)
Theorem	fin1a2s 10367*	An II-infinite set can have an I-infinite part broken off and remain II-infinite. (Contributed by Stefan O'Rear, 8-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ ((𝐴 ∈ 𝑉 ∧ ∀𝑥 ∈ 𝒫 𝐴(𝑥 ∈ Fin ∨ (𝐴 ∖ 𝑥) ∈ FinII)) → 𝐴 ∈ FinII)
Theorem	fin1a2 10368	Every Ia-finite set is II-finite. Theorem 1 of [Levy58], p. 3. (Contributed by Stefan O'Rear, 8-Nov-2014.) (Proof shortened by Mario Carneiro, 17-May-2015.)
⊢ (𝐴 ∈ FinIa → 𝐴 ∈ FinII)
2.6.17  Hereditarily size-limited sets without Choice
Theorem	itunifval 10369*	Function value of iterated unions. EDITORIAL: The iterated unions and order types of ordered sets are split out here because they could conceivably be independently useful. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ (𝐴 ∈ 𝑉 → (𝑈‘𝐴) = (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝐴) ↾ ω))
Theorem	itunifn 10370*	Functionality of the iterated union. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ (𝐴 ∈ 𝑉 → (𝑈‘𝐴) Fn ω)
Theorem	ituni0 10371*	A zero-fold iterated union. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ (𝐴 ∈ 𝑉 → ((𝑈‘𝐴)‘∅) = 𝐴)
Theorem	itunisuc 10372*	Successor iterated union. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ ((𝑈‘𝐴)‘suc 𝐵) = ∪ ((𝑈‘𝐴)‘𝐵)
Theorem	itunitc1 10373*	Each union iterate is a member of the transitive closure. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ ((𝑈‘𝐴)‘𝐵) ⊆ (TC‘𝐴)
Theorem	itunitc 10374*	The union of all union iterates creates the transitive closure; compare trcl 9681. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ (TC‘𝐴) = ∪ ran (𝑈‘𝐴)
Theorem	ituniiun 10375*	Unwrap an iterated union from the "other end". (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    ⇒   ⊢ (𝐴 ∈ 𝑉 → ((𝑈‘𝐴)‘suc 𝐵) = ∪ 𝑎 ∈ 𝐴 ((𝑈‘𝑎)‘𝐵))
Theorem	hsmexlem7 10376*	Lemma for hsmex 10385. Properties of the recurrent sequence of ordinals. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ 𝐻 = (rec((𝑧 ∈ V ↦ (har‘𝒫 (𝑋 × 𝑧))), (har‘𝒫 𝑋)) ↾ ω)    ⇒   ⊢ (𝐻‘∅) = (har‘𝒫 𝑋)
Theorem	hsmexlem8 10377*	Lemma for hsmex 10385. Properties of the recurrent sequence of ordinals. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ 𝐻 = (rec((𝑧 ∈ V ↦ (har‘𝒫 (𝑋 × 𝑧))), (har‘𝒫 𝑋)) ↾ ω)    ⇒   ⊢ (𝑎 ∈ ω → (𝐻‘suc 𝑎) = (har‘𝒫 (𝑋 × (𝐻‘𝑎))))
Theorem	hsmexlem9 10378*	Lemma for hsmex 10385. Properties of the recurrent sequence of ordinals. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ 𝐻 = (rec((𝑧 ∈ V ↦ (har‘𝒫 (𝑋 × 𝑧))), (har‘𝒫 𝑋)) ↾ ω)    ⇒   ⊢ (𝑎 ∈ ω → (𝐻‘𝑎) ∈ On)
Theorem	hsmexlem1 10379	Lemma for hsmex 10385. Bound the order type of a limited-cardinality set of ordinals. (Contributed by Stefan O'Rear, 14-Feb-2015.) (Revised by Mario Carneiro, 26-Jun-2015.)
⊢ 𝑂 = OrdIso( E , 𝐴)    ⇒   ⊢ ((𝐴 ⊆ On ∧ 𝐴 ≼* 𝐵) → dom 𝑂 ∈ (har‘𝒫 𝐵))
Theorem	hsmexlem2 10380*	Lemma for hsmex 10385. Bound the order type of a union of sets of ordinals, each of limited order type. Vaguely reminiscent of unictb 10528 but use of order types allows to canonically choose the sub-bijections, removing the choice requirement. (Contributed by Stefan O'Rear, 14-Feb-2015.) (Revised by Mario Carneiro, 26-Jun-2015.) (Revised by AV, 18-Sep-2021.)
⊢ 𝐹 = OrdIso( E , 𝐵)    &   ⊢ 𝐺 = OrdIso( E , ∪ 𝑎 ∈ 𝐴 𝐵)    ⇒   ⊢ ((𝐴 ∈ 𝑉 ∧ 𝐶 ∈ On ∧ ∀𝑎 ∈ 𝐴 (𝐵 ∈ 𝒫 On ∧ dom 𝐹 ∈ 𝐶)) → dom 𝐺 ∈ (har‘𝒫 (𝐴 × 𝐶)))
Theorem	hsmexlem3 10381*	Lemma for hsmex 10385. Clear 𝐼 hypothesis and extend previous result by dominance. Note that this could be substantially strengthened, e.g., using the weak Hartogs function, but all we need here is that there be *some* dominating ordinal. (Contributed by Stefan O'Rear, 14-Feb-2015.) (Revised by Mario Carneiro, 26-Jun-2015.)
⊢ 𝐹 = OrdIso( E , 𝐵)    &   ⊢ 𝐺 = OrdIso( E , ∪ 𝑎 ∈ 𝐴 𝐵)    ⇒   ⊢ (((𝐴 ≼* 𝐷 ∧ 𝐶 ∈ On) ∧ ∀𝑎 ∈ 𝐴 (𝐵 ∈ 𝒫 On ∧ dom 𝐹 ∈ 𝐶)) → dom 𝐺 ∈ (har‘𝒫 (𝐷 × 𝐶)))
Theorem	hsmexlem4 10382*	Lemma for hsmex 10385. The core induction, establishing bounds on the order types of iterated unions of the initial set. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ 𝑋 ∈ V    &   ⊢ 𝐻 = (rec((𝑧 ∈ V ↦ (har‘𝒫 (𝑋 × 𝑧))), (har‘𝒫 𝑋)) ↾ ω)    &   ⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    &   ⊢ 𝑆 = {𝑎 ∈ ∪ (𝑅1 “ On) ∣ ∀𝑏 ∈ (TC‘{𝑎})𝑏 ≼ 𝑋}    &   ⊢ 𝑂 = OrdIso( E , (rank “ ((𝑈‘𝑑)‘𝑐)))    ⇒   ⊢ ((𝑐 ∈ ω ∧ 𝑑 ∈ 𝑆) → dom 𝑂 ∈ (𝐻‘𝑐))
Theorem	hsmexlem5 10383*	Lemma for hsmex 10385. Combining the above constraints, along with itunitc 10374 and tcrank 9837, gives an effective constraint on the rank of 𝑆. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ 𝑋 ∈ V    &   ⊢ 𝐻 = (rec((𝑧 ∈ V ↦ (har‘𝒫 (𝑋 × 𝑧))), (har‘𝒫 𝑋)) ↾ ω)    &   ⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    &   ⊢ 𝑆 = {𝑎 ∈ ∪ (𝑅1 “ On) ∣ ∀𝑏 ∈ (TC‘{𝑎})𝑏 ≼ 𝑋}    &   ⊢ 𝑂 = OrdIso( E , (rank “ ((𝑈‘𝑑)‘𝑐)))    ⇒   ⊢ (𝑑 ∈ 𝑆 → (rank‘𝑑) ∈ (har‘𝒫 (ω × ∪ ran 𝐻)))
Theorem	hsmexlem6 10384*	Lemma for hsmex 10385. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ 𝑋 ∈ V    &   ⊢ 𝐻 = (rec((𝑧 ∈ V ↦ (har‘𝒫 (𝑋 × 𝑧))), (har‘𝒫 𝑋)) ↾ ω)    &   ⊢ 𝑈 = (𝑥 ∈ V ↦ (rec((𝑦 ∈ V ↦ ∪ 𝑦), 𝑥) ↾ ω))    &   ⊢ 𝑆 = {𝑎 ∈ ∪ (𝑅1 “ On) ∣ ∀𝑏 ∈ (TC‘{𝑎})𝑏 ≼ 𝑋}    &   ⊢ 𝑂 = OrdIso( E , (rank “ ((𝑈‘𝑑)‘𝑐)))    ⇒   ⊢ 𝑆 ∈ V
Theorem	hsmex 10385*	The collection of hereditarily size-limited well-founded sets comprise a set. The proof is that of Randall Holmes at http://math.boisestate.edu/~holmes/holmes/hereditary.pdf, with modifications to use Hartogs' theorem instead of the weak variant (inconsequentially weakening some intermediate results), and making the well-foundedness condition explicit to avoid a direct dependence on ax-reg 9545. (Contributed by Stefan O'Rear, 14-Feb-2015.)
⊢ (𝑋 ∈ 𝑉 → {𝑠 ∈ ∪ (𝑅1 “ On) ∣ ∀𝑥 ∈ (TC‘{𝑠})𝑥 ≼ 𝑋} ∈ V)
Theorem	hsmex2 10386*	The set of hereditary size-limited sets, assuming ax-reg 9545. (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ (𝑋 ∈ 𝑉 → {𝑠 ∣ ∀𝑥 ∈ (TC‘{𝑠})𝑥 ≼ 𝑋} ∈ V)
Theorem	hsmex3 10387*	The set of hereditary size-limited sets, assuming ax-reg 9545, using strict comparison (an easy corollary by separation). (Contributed by Stefan O'Rear, 11-Feb-2015.)
⊢ (𝑋 ∈ 𝑉 → {𝑠 ∣ ∀𝑥 ∈ (TC‘{𝑠})𝑥 ≺ 𝑋} ∈ V)
PART 3  ZFC (ZERMELO-FRAENKEL WITH CHOICE) SET THEORY In this section we add the Axiom of Choice ax-ac 10412, as well as weaker forms such as the axiom of countable choice ax-cc 10388 and dependent choice ax-dc 10399. We introduce these weaker forms so that theorems that do not need the full power of the axiom of choice, but need more than simple ZF, can use these intermediate axioms instead. The combination of the Zermelo-Fraenkel axioms and the axiom of choice is often abbreviated as ZFC. The axiom of choice is widely accepted, and ZFC is the most commonly-accepted fundamental set of axioms for mathematics. However, there have been and still are some lingering controversies about the Axiom of Choice. The axiom of choice does not satisfy those who wish to have a constructive proof (e.g., it will not satisfy intuitionistic logic). Thus, we make it easy to identify which proofs depend on the axiom of choice or its weaker forms.
3.1  ZFC Set Theory - add Countable Choice and Dependent Choice
3.1.1  Introduce the Axiom of Countable Choice
Axiom	ax-cc 10388*	The axiom of countable choice (CC), also known as the axiom of denumerable choice. It is clearly a special case of ac5 10430, but is weak enough that it can be proven using DC (see axcc 10411). It is, however, strictly stronger than ZF and cannot be proven in ZF. It states that any countable collection of nonempty sets must have a choice function. (Contributed by Mario Carneiro, 9-Feb-2013.)
⊢ (𝑥 ≈ ω → ∃𝑓∀𝑧 ∈ 𝑥 (𝑧 ≠ ∅ → (𝑓‘𝑧) ∈ 𝑧))
Theorem	axcc2lem 10389*	Lemma for axcc2 10390. (Contributed by Mario Carneiro, 8-Feb-2013.)
⊢ 𝐾 = (𝑛 ∈ ω ↦ if((𝐹‘𝑛) = ∅, {∅}, (𝐹‘𝑛)))    &   ⊢ 𝐴 = (𝑛 ∈ ω ↦ ({𝑛} × (𝐾‘𝑛)))    &   ⊢ 𝐺 = (𝑛 ∈ ω ↦ (2nd ‘(𝑓‘(𝐴‘𝑛))))    ⇒   ⊢ ∃𝑔(𝑔 Fn ω ∧ ∀𝑛 ∈ ω ((𝐹‘𝑛) ≠ ∅ → (𝑔‘𝑛) ∈ (𝐹‘𝑛)))
Theorem	axcc2 10390*	A possibly more useful version of ax-cc using sequences instead of countable sets. The Axiom of Infinity is needed to prove this, and indeed this implies the Axiom of Infinity. (Contributed by Mario Carneiro, 8-Feb-2013.)
⊢ ∃𝑔(𝑔 Fn ω ∧ ∀𝑛 ∈ ω ((𝐹‘𝑛) ≠ ∅ → (𝑔‘𝑛) ∈ (𝐹‘𝑛)))
Theorem	axcc3 10391*	A possibly more useful version of ax-cc 10388 using sequences 𝐹(𝑛) instead of countable sets. The Axiom of Infinity is needed to prove this, and indeed this implies the Axiom of Infinity. (Contributed by Mario Carneiro, 8-Feb-2013.) (Revised by Mario Carneiro, 26-Dec-2014.)
⊢ 𝐹 ∈ V    &   ⊢ 𝑁 ≈ ω    ⇒   ⊢ ∃𝑓(𝑓 Fn 𝑁 ∧ ∀𝑛 ∈ 𝑁 (𝐹 ≠ ∅ → (𝑓‘𝑛) ∈ 𝐹))
Theorem	axcc4 10392*	A version of axcc3 10391 that uses wffs instead of classes. (Contributed by Mario Carneiro, 7-Apr-2013.)
⊢ 𝐴 ∈ V    &   ⊢ 𝑁 ≈ ω    &   ⊢ (𝑥 = (𝑓‘𝑛) → (𝜑 ↔ 𝜓))    ⇒   ⊢ (∀𝑛 ∈ 𝑁 ∃𝑥 ∈ 𝐴 𝜑 → ∃𝑓(𝑓:𝑁⟶𝐴 ∧ ∀𝑛 ∈ 𝑁 𝜓))
Theorem	acncc 10393	An ax-cc 10388 equivalent: every set has choice sets of length ω. (Contributed by Mario Carneiro, 31-Aug-2015.)
⊢ AC ω = V
Theorem	axcc4dom 10394*	Relax the constraint on axcc4 10392 to dominance instead of equinumerosity. (Contributed by Mario Carneiro, 18-Jan-2014.)
⊢ 𝐴 ∈ V    &   ⊢ (𝑥 = (𝑓‘𝑛) → (𝜑 ↔ 𝜓))    ⇒   ⊢ ((𝑁 ≼ ω ∧ ∀𝑛 ∈ 𝑁 ∃𝑥 ∈ 𝐴 𝜑) → ∃𝑓(𝑓:𝑁⟶𝐴 ∧ ∀𝑛 ∈ 𝑁 𝜓))
Theorem	domtriomlem 10395*	Lemma for domtriom 10396. (Contributed by Mario Carneiro, 9-Feb-2013.)
⊢ 𝐴 ∈ V    &   ⊢ 𝐵 = {𝑦 ∣ (𝑦 ⊆ 𝐴 ∧ 𝑦 ≈ 𝒫 𝑛)}    &   ⊢ 𝐶 = (𝑛 ∈ ω ↦ ((𝑏‘𝑛) ∖ ∪ 𝑘 ∈ 𝑛 (𝑏‘𝑘)))    ⇒   ⊢ (¬ 𝐴 ∈ Fin → ω ≼ 𝐴)
Theorem	domtriom 10396	Trichotomy of equinumerosity for ω, proven using countable choice. Equivalently, all Dedekind-finite sets (as in isfin4-2 10267) are finite in the usual sense and conversely. (Contributed by Mario Carneiro, 9-Feb-2013.)
⊢ 𝐴 ∈ V    ⇒   ⊢ (ω ≼ 𝐴 ↔ ¬ 𝐴 ≺ ω)
Theorem	fin41 10397	Under countable choice, the IV-finite sets (Dedekind-finite) coincide with I-finite (finite in the usual sense) sets. (Contributed by Mario Carneiro, 16-May-2015.)
⊢ FinIV = Fin
Theorem	dominf 10398	A nonempty set that is a subset of its union is infinite. This version is proved from ax-cc 10388. See dominfac 10526 for a version proved from ax-ac 10412. The axiom of Regularity is used for this proof, via inf3lem6 9586, and its use is necessary: otherwise the set 𝐴 = {𝐴} or 𝐴 = {∅, 𝐴} (where the second example even has nonempty well-founded part) provides a counterexample. (Contributed by Mario Carneiro, 9-Feb-2013.)
⊢ 𝐴 ∈ V    ⇒   ⊢ ((𝐴 ≠ ∅ ∧ 𝐴 ⊆ ∪ 𝐴) → ω ≼ 𝐴)
3.1.2  Introduce the Axiom of Dependent Choice
Axiom	ax-dc 10399*	Dependent Choice. Axiom DC1 of [Schechter] p. 149. 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. Dependent choice is equivalent to the statement that every (nonempty) pruned tree has a branch. This axiom is redundant in ZFC; see axdc 10474. But ZF+DC is strictly weaker than ZF+AC, so this axiom provides for theorems that do not need the full power of AC. (Contributed by Mario Carneiro, 25-Jan-2013.)
⊢ ((∃𝑦∃𝑧 𝑦𝑥𝑧 ∧ ran 𝑥 ⊆ dom 𝑥) → ∃𝑓∀𝑛 ∈ ω (𝑓‘𝑛)𝑥(𝑓‘suc 𝑛))
Theorem	dcomex 10400	The Axiom of Dependent Choice implies Infinity, the way we have stated it. Thus, we have Inf+AC implies DC and DC implies Inf, but AC does not imply Inf. (Contributed by Mario Carneiro, 25-Jan-2013.)
⊢ ω ∈ V