Metamath Proof Explorer


Theorem tz6.12-1OLD

Description: Obsolete version of tz6.12-1 as of 23-Dec-2024. (Contributed by NM, 30-Apr-2004) (Proof modification is discouraged.) (New usage is discouraged.)

Ref Expression
Assertion tz6.12-1OLD A F y ∃! y A F y F A = y

Proof

Step Hyp Ref Expression
1 df-fv F A = ι y | A F y
2 iota1 ∃! y A F y A F y ι y | A F y = y
3 2 biimpac A F y ∃! y A F y ι y | A F y = y
4 1 3 eqtrid A F y ∃! y A F y F A = y