Metamath Proof Explorer


Theorem modelaxrep

Description: Conditions which guarantee that a class models the Axiom of Replacement ax-rep . Similar to Lemma II.2.4(6) of Kunen2 p. 111. The first two hypotheses are those in Kunen. The reason for the third hypothesis that our version of Replacement is different from Kunen's (which is zfrep6 ). If we assumed Regularity, we could eliminate this extra hypothesis, since under Regularity, the empty set is a member of every non-empty transitive class.

Note that, to obtain the relativization of an instance of Replacement to M , the formula A. y ph would need to be replaced with A. y e. M ch , where ch is ph with all quantifiers relativized to M . However, we can obtain this by using y e. M /\ ch for ph in this theorem, so it does establish that all instances of Replacement hold in M . (Contributed by Eric Schmidt, 29-Sep-2025)

Ref Expression
Hypotheses modelaxrep.1 ( 𝜓 → Tr 𝑀 )
modelaxrep.2 ( 𝜓 → ∀ 𝑓 ( ( Fun 𝑓 ∧ dom 𝑓𝑀 ∧ ran 𝑓𝑀 ) → ran 𝑓𝑀 ) )
modelaxrep.3 ( 𝜓 → ∅ ∈ 𝑀 )
Assertion modelaxrep ( 𝜓 → ∀ 𝑥𝑀 ( ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) → ∃ 𝑦𝑀𝑧𝑀 ( 𝑧𝑦 ↔ ∃ 𝑤𝑀 ( 𝑤𝑥 ∧ ∀ 𝑦 𝜑 ) ) ) )

Proof

Step Hyp Ref Expression
1 modelaxrep.1 ( 𝜓 → Tr 𝑀 )
2 modelaxrep.2 ( 𝜓 → ∀ 𝑓 ( ( Fun 𝑓 ∧ dom 𝑓𝑀 ∧ ran 𝑓𝑀 ) → ran 𝑓𝑀 ) )
3 modelaxrep.3 ( 𝜓 → ∅ ∈ 𝑀 )
4 funeq ( 𝑓 = 𝑔 → ( Fun 𝑓 ↔ Fun 𝑔 ) )
5 dmeq ( 𝑓 = 𝑔 → dom 𝑓 = dom 𝑔 )
6 5 eleq1d ( 𝑓 = 𝑔 → ( dom 𝑓𝑀 ↔ dom 𝑔𝑀 ) )
7 rneq ( 𝑓 = 𝑔 → ran 𝑓 = ran 𝑔 )
8 7 sseq1d ( 𝑓 = 𝑔 → ( ran 𝑓𝑀 ↔ ran 𝑔𝑀 ) )
9 4 6 8 3anbi123d ( 𝑓 = 𝑔 → ( ( Fun 𝑓 ∧ dom 𝑓𝑀 ∧ ran 𝑓𝑀 ) ↔ ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) ) )
10 7 eleq1d ( 𝑓 = 𝑔 → ( ran 𝑓𝑀 ↔ ran 𝑔𝑀 ) )
11 9 10 imbi12d ( 𝑓 = 𝑔 → ( ( ( Fun 𝑓 ∧ dom 𝑓𝑀 ∧ ran 𝑓𝑀 ) → ran 𝑓𝑀 ) ↔ ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) )
12 11 cbvalvw ( ∀ 𝑓 ( ( Fun 𝑓 ∧ dom 𝑓𝑀 ∧ ran 𝑓𝑀 ) → ran 𝑓𝑀 ) ↔ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) )
13 2 12 sylib ( 𝜓 → ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) )
14 trss ( Tr 𝑀 → ( 𝑥𝑀𝑥𝑀 ) )
15 14 imp ( ( Tr 𝑀𝑥𝑀 ) → 𝑥𝑀 )
16 15 ad5ant14 ( ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) → 𝑥𝑀 )
17 simp-4r ( ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) → ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) )
18 simpllr ( ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) → ∅ ∈ 𝑀 )
19 simplr ( ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) → 𝑥𝑀 )
20 nfv 𝑤 ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 )
21 nfra1 𝑤𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 )
22 20 21 nfan 𝑤 ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) )
23 nfv 𝑧 ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 )
24 nfcv 𝑧 𝑀
25 nfra1 𝑧𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 )
26 24 25 nfrexw 𝑧𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 )
27 24 26 nfralw 𝑧𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 )
28 23 27 nfan 𝑧 ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) )
29 nfopab2 𝑧 { ⟨ 𝑤 , 𝑧 ⟩ ∣ ( 𝑤𝑥 ∧ ( 𝑧𝑀 ∧ ∀ 𝑦 𝜑 ) ) }
30 eqid { ⟨ 𝑤 , 𝑧 ⟩ ∣ ( 𝑤𝑥 ∧ ( 𝑧𝑀 ∧ ∀ 𝑦 𝜑 ) ) } = { ⟨ 𝑤 , 𝑧 ⟩ ∣ ( 𝑤𝑥 ∧ ( 𝑧𝑀 ∧ ∀ 𝑦 𝜑 ) ) }
31 rsp ( ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) → ( 𝑤𝑀 → ∃ 𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) )
32 31 adantl ( ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) → ( 𝑤𝑀 → ∃ 𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) )
33 16 17 18 19 22 28 29 30 32 modelaxreplem3 ( ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) ∧ ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) ) → ∃ 𝑦𝑀𝑧𝑀 ( 𝑧𝑦 ↔ ∃ 𝑤𝑀 ( 𝑤𝑥 ∧ ∀ 𝑦 𝜑 ) ) )
34 33 ex ( ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) ∧ 𝑥𝑀 ) → ( ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) → ∃ 𝑦𝑀𝑧𝑀 ( 𝑧𝑦 ↔ ∃ 𝑤𝑀 ( 𝑤𝑥 ∧ ∀ 𝑦 𝜑 ) ) ) )
35 34 ralrimiva ( ( ( Tr 𝑀 ∧ ∀ 𝑔 ( ( Fun 𝑔 ∧ dom 𝑔𝑀 ∧ ran 𝑔𝑀 ) → ran 𝑔𝑀 ) ) ∧ ∅ ∈ 𝑀 ) → ∀ 𝑥𝑀 ( ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) → ∃ 𝑦𝑀𝑧𝑀 ( 𝑧𝑦 ↔ ∃ 𝑤𝑀 ( 𝑤𝑥 ∧ ∀ 𝑦 𝜑 ) ) ) )
36 1 13 3 35 syl21anc ( 𝜓 → ∀ 𝑥𝑀 ( ∀ 𝑤𝑀𝑦𝑀𝑧𝑀 ( ∀ 𝑦 𝜑𝑧 = 𝑦 ) → ∃ 𝑦𝑀𝑧𝑀 ( 𝑧𝑦 ↔ ∃ 𝑤𝑀 ( 𝑤𝑥 ∧ ∀ 𝑦 𝜑 ) ) ) )