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Metamath Proof Explorer

Theorem f1stres

Description: Mapping of a restriction of the 1st (first member of an ordered pair) function. (Contributed by NM, 11-Oct-2004) (Revised by Mario Carneiro, 8-Sep-2013)

Ref Expression
Assertion f1stres ( 1st ↾ ( 𝐴 × 𝐵 ) ) : ( 𝐴 × 𝐵 ) ⟶ 𝐴

Proof

Step Hyp Ref Expression
1 vex ⊢ 𝑦 ∈ V
2 vex ⊢ 𝑧 ∈ V
3 1 2 op1sta ⊢ ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } = 𝑦
4 3 eleq1i ⊢ ( ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } ∈ 𝐴 ↔ 𝑦 ∈ 𝐴 )
5 4 biimpri ⊢ ( 𝑦 ∈ 𝐴 → ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } ∈ 𝐴 )
6 5 adantr ⊢ ( ( 𝑦 ∈ 𝐴 ∧ 𝑧 ∈ 𝐵 ) → ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } ∈ 𝐴 )
7 6 rgen2 ⊢ ∀ 𝑦 ∈ 𝐴 ∀ 𝑧 ∈ 𝐵 ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } ∈ 𝐴
8 sneq ⊢ ( 𝑥 = ⟨ 𝑦 , 𝑧 ⟩ → { 𝑥 } = { ⟨ 𝑦 , 𝑧 ⟩ } )
9 8 dmeqd ⊢ ( 𝑥 = ⟨ 𝑦 , 𝑧 ⟩ → dom { 𝑥 } = dom { ⟨ 𝑦 , 𝑧 ⟩ } )
10 9 unieqd ⊢ ( 𝑥 = ⟨ 𝑦 , 𝑧 ⟩ → ∪ dom { 𝑥 } = ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } )
11 10 eleq1d ⊢ ( 𝑥 = ⟨ 𝑦 , 𝑧 ⟩ → ( ∪ dom { 𝑥 } ∈ 𝐴 ↔ ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } ∈ 𝐴 ) )
12 11 ralxp ⊢ ( ∀ 𝑥 ∈ ( 𝐴 × 𝐵 ) ∪ dom { 𝑥 } ∈ 𝐴 ↔ ∀ 𝑦 ∈ 𝐴 ∀ 𝑧 ∈ 𝐵 ∪ dom { ⟨ 𝑦 , 𝑧 ⟩ } ∈ 𝐴 )
13 7 12 mpbir ⊢ ∀ 𝑥 ∈ ( 𝐴 × 𝐵 ) ∪ dom { 𝑥 } ∈ 𝐴
14 df-1st ⊢ 1st = ( 𝑥 ∈ V ↦ ∪ dom { 𝑥 } )
15 14 reseq1i ⊢ ( 1st ↾ ( 𝐴 × 𝐵 ) ) = ( ( 𝑥 ∈ V ↦ ∪ dom { 𝑥 } ) ↾ ( 𝐴 × 𝐵 ) )
16 ssv ⊢ ( 𝐴 × 𝐵 ) ⊆ V
17 resmpt ⊢ ( ( 𝐴 × 𝐵 ) ⊆ V → ( ( 𝑥 ∈ V ↦ ∪ dom { 𝑥 } ) ↾ ( 𝐴 × 𝐵 ) ) = ( 𝑥 ∈ ( 𝐴 × 𝐵 ) ↦ ∪ dom { 𝑥 } ) )
18 16 17 ax-mp ⊢ ( ( 𝑥 ∈ V ↦ ∪ dom { 𝑥 } ) ↾ ( 𝐴 × 𝐵 ) ) = ( 𝑥 ∈ ( 𝐴 × 𝐵 ) ↦ ∪ dom { 𝑥 } )
19 15 18 eqtri ⊢ ( 1st ↾ ( 𝐴 × 𝐵 ) ) = ( 𝑥 ∈ ( 𝐴 × 𝐵 ) ↦ ∪ dom { 𝑥 } )
20 19 fmpt ⊢ ( ∀ 𝑥 ∈ ( 𝐴 × 𝐵 ) ∪ dom { 𝑥 } ∈ 𝐴 ↔ ( 1st ↾ ( 𝐴 × 𝐵 ) ) : ( 𝐴 × 𝐵 ) ⟶ 𝐴 )
21 13 20 mpbi ⊢ ( 1st ↾ ( 𝐴 × 𝐵 ) ) : ( 𝐴 × 𝐵 ) ⟶ 𝐴