Metamath Proof Explorer


Theorem cocossss

Description: Two ways of saying that cosets by cosets by R is a subclass. (Contributed by Peter Mazsa, 17-Sep-2021)

Ref Expression
Assertion cocossss ( ≀ ≀ 𝑅𝑆 ↔ ∀ 𝑥𝑦𝑧 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )

Proof

Step Hyp Ref Expression
1 relcoss Rel ≀ ≀ 𝑅
2 ssrel3 ( Rel ≀ ≀ 𝑅 → ( ≀ ≀ 𝑅𝑆 ↔ ∀ 𝑥𝑧 ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) ) )
3 1 2 ax-mp ( ≀ ≀ 𝑅𝑆 ↔ ∀ 𝑥𝑧 ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) )
4 brcoss ( ( 𝑥 ∈ V ∧ 𝑧 ∈ V ) → ( 𝑥 ≀ ≀ 𝑅 𝑧 ↔ ∃ 𝑦 ( 𝑦𝑅 𝑥𝑦𝑅 𝑧 ) ) )
5 4 el2v ( 𝑥 ≀ ≀ 𝑅 𝑧 ↔ ∃ 𝑦 ( 𝑦𝑅 𝑥𝑦𝑅 𝑧 ) )
6 brcosscnvcoss ( ( 𝑦 ∈ V ∧ 𝑥 ∈ V ) → ( 𝑦𝑅 𝑥𝑥𝑅 𝑦 ) )
7 6 el2v ( 𝑦𝑅 𝑥𝑥𝑅 𝑦 )
8 7 anbi1i ( ( 𝑦𝑅 𝑥𝑦𝑅 𝑧 ) ↔ ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) )
9 8 exbii ( ∃ 𝑦 ( 𝑦𝑅 𝑥𝑦𝑅 𝑧 ) ↔ ∃ 𝑦 ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) )
10 5 9 bitri ( 𝑥 ≀ ≀ 𝑅 𝑧 ↔ ∃ 𝑦 ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) )
11 10 imbi1i ( ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) ↔ ( ∃ 𝑦 ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
12 19.23v ( ∀ 𝑦 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) ↔ ( ∃ 𝑦 ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
13 11 12 bitr4i ( ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) ↔ ∀ 𝑦 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
14 13 albii ( ∀ 𝑧 ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) ↔ ∀ 𝑧𝑦 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
15 alcom ( ∀ 𝑧𝑦 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) ↔ ∀ 𝑦𝑧 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
16 14 15 bitri ( ∀ 𝑧 ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) ↔ ∀ 𝑦𝑧 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
17 16 albii ( ∀ 𝑥𝑧 ( 𝑥 ≀ ≀ 𝑅 𝑧𝑥 𝑆 𝑧 ) ↔ ∀ 𝑥𝑦𝑧 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )
18 3 17 bitri ( ≀ ≀ 𝑅𝑆 ↔ ∀ 𝑥𝑦𝑧 ( ( 𝑥𝑅 𝑦𝑦𝑅 𝑧 ) → 𝑥 𝑆 𝑧 ) )