Metamath Proof Explorer


Theorem bj-restsnss2

Description: Special case of bj-restsn . (Contributed by BJ, 27-Apr-2021)

Ref Expression
Assertion bj-restsnss2 ( ( 𝐴𝑉𝑌𝐴 ) → ( { 𝑌 } ↾t 𝐴 ) = { 𝑌 } )

Proof

Step Hyp Ref Expression
1 df-ss ( 𝑌𝐴 ↔ ( 𝑌𝐴 ) = 𝑌 )
2 sneq ( ( 𝑌𝐴 ) = 𝑌 → { ( 𝑌𝐴 ) } = { 𝑌 } )
3 1 2 sylbi ( 𝑌𝐴 → { ( 𝑌𝐴 ) } = { 𝑌 } )
4 ssexg ( ( 𝑌𝐴𝐴𝑉 ) → 𝑌 ∈ V )
5 4 ancoms ( ( 𝐴𝑉𝑌𝐴 ) → 𝑌 ∈ V )
6 bj-restsn ( ( 𝑌 ∈ V ∧ 𝐴𝑉 ) → ( { 𝑌 } ↾t 𝐴 ) = { ( 𝑌𝐴 ) } )
7 6 ancoms ( ( 𝐴𝑉𝑌 ∈ V ) → ( { 𝑌 } ↾t 𝐴 ) = { ( 𝑌𝐴 ) } )
8 5 7 syldan ( ( 𝐴𝑉𝑌𝐴 ) → ( { 𝑌 } ↾t 𝐴 ) = { ( 𝑌𝐴 ) } )
9 eqeq2 ( { ( 𝑌𝐴 ) } = { 𝑌 } → ( ( { 𝑌 } ↾t 𝐴 ) = { ( 𝑌𝐴 ) } ↔ ( { 𝑌 } ↾t 𝐴 ) = { 𝑌 } ) )
10 9 biimpa ( ( { ( 𝑌𝐴 ) } = { 𝑌 } ∧ ( { 𝑌 } ↾t 𝐴 ) = { ( 𝑌𝐴 ) } ) → ( { 𝑌 } ↾t 𝐴 ) = { 𝑌 } )
11 3 8 10 syl2an2 ( ( 𝐴𝑉𝑌𝐴 ) → ( { 𝑌 } ↾t 𝐴 ) = { 𝑌 } )