Metamath Proof Explorer


Theorem uniex2

Description: The Axiom of Union using the standard abbreviation for union. Given any set x , its union y exists. (Contributed by NM, 4-Jun-2006)

Ref Expression
Assertion uniex2 𝑦 𝑦 = 𝑥

Proof

Step Hyp Ref Expression
1 ax-un 𝑦𝑧 ( ∃ 𝑤 ( 𝑧𝑤𝑤𝑥 ) → 𝑧𝑦 )
2 eluni ( 𝑧 𝑥 ↔ ∃ 𝑤 ( 𝑧𝑤𝑤𝑥 ) )
3 2 imbi1i ( ( 𝑧 𝑥𝑧𝑦 ) ↔ ( ∃ 𝑤 ( 𝑧𝑤𝑤𝑥 ) → 𝑧𝑦 ) )
4 3 albii ( ∀ 𝑧 ( 𝑧 𝑥𝑧𝑦 ) ↔ ∀ 𝑧 ( ∃ 𝑤 ( 𝑧𝑤𝑤𝑥 ) → 𝑧𝑦 ) )
5 4 exbii ( ∃ 𝑦𝑧 ( 𝑧 𝑥𝑧𝑦 ) ↔ ∃ 𝑦𝑧 ( ∃ 𝑤 ( 𝑧𝑤𝑤𝑥 ) → 𝑧𝑦 ) )
6 1 5 mpbir 𝑦𝑧 ( 𝑧 𝑥𝑧𝑦 )
7 6 bm1.3ii 𝑦𝑧 ( 𝑧𝑦𝑧 𝑥 )
8 dfcleq ( 𝑦 = 𝑥 ↔ ∀ 𝑧 ( 𝑧𝑦𝑧 𝑥 ) )
9 8 exbii ( ∃ 𝑦 𝑦 = 𝑥 ↔ ∃ 𝑦𝑧 ( 𝑧𝑦𝑧 𝑥 ) )
10 7 9 mpbir 𝑦 𝑦 = 𝑥