Theorem snjust 3380

Description: Soundness justification theorem for df-sn 3381. (Contributed by Rodolfo Medina, 28-Apr-2010.) (Proof shortened by Andrew Salmon, 29-Jun-2011.)

Assertion

Ref	Expression
snjust	|- { x | x = A } = { y | y = A }

Distinct variable groups:   x, A   y, A

Proof of Theorem snjust

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		eqeq1 2046	. . 3 |- ( x = z -> ( x = A <-> z = A ) )
2	1	cbvabv 2161	. 2 |- { x | x = A } = { z | z = A }
3		eqeq1 2046	. . 3 |- ( z = y -> ( z = A <-> y = A ) )
4	3	cbvabv 2161	. 2 |- { z | z = A } = { y | y = A }
5	2, 4	eqtri 2060	1 |- { x | x = A } = { y | y = A }

Syntax hints:   = wceq 1243   {cab 2026

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022

This theorem depends on definitions:  df-bi 110  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033

This theorem is referenced by: (None)