Metamath Proof Explorer


Theorem iotaval

Description: Theorem 8.19 in Quine p. 57. This theorem is the fundamental property of iota. (Contributed by Andrew Salmon, 11-Jul-2011) Remove dependency on ax-10 , ax-11 , ax-12 . (Revised by SN, 23-Nov-2024)

Ref Expression
Assertion iotaval ( ∀ 𝑥 ( 𝜑𝑥 = 𝑦 ) → ( ℩ 𝑥 𝜑 ) = 𝑦 )

Proof

Step Hyp Ref Expression
1 abbi ( ∀ 𝑥 ( 𝜑𝑥 = 𝑦 ) → { 𝑥𝜑 } = { 𝑥𝑥 = 𝑦 } )
2 df-sn { 𝑦 } = { 𝑥𝑥 = 𝑦 }
3 1 2 eqtr4di ( ∀ 𝑥 ( 𝜑𝑥 = 𝑦 ) → { 𝑥𝜑 } = { 𝑦 } )
4 iotaval2 ( { 𝑥𝜑 } = { 𝑦 } → ( ℩ 𝑥 𝜑 ) = 𝑦 )
5 3 4 syl ( ∀ 𝑥 ( 𝜑𝑥 = 𝑦 ) → ( ℩ 𝑥 𝜑 ) = 𝑦 )