Theorem dfpr2 3750

Description: Alternate definition of unordered pair. Definition 5.1 of [TakeutiZaring] p. 15. (Contributed by NM, 24-Apr-1994.)

Assertion

Ref	Expression
dfpr2	|- {A, B} = {x | (x = A \/ x = B)}

Distinct variable groups:   x,A   x,B

Proof of Theorem dfpr2

Step	Hyp	Ref	Expression
1		df-pr 3743	. 2 |- {A, B} = ({A} u. {B})
2		elun 3221	. . . 4 |- (x e. ({A} u. {B}) <-> (x e. {A} \/ x e. {B}))
3		elsn 3749	. . . . 5 |- (x e. {A} <-> x = A)
4		elsn 3749	. . . . 5 |- (x e. {B} <-> x = B)
5	3, 4	orbi12i 507	. . . 4 |- ((x e. {A} \/ x e. {B}) <-> (x = A \/ x = B))
6	2, 5	bitri 240	. . 3 |- (x e. ({A} u. {B}) <-> (x = A \/ x = B))
7	6	abbi2i 2465	. 2 |- ({A} u. {B}) = {x | (x = A \/ x = B)}
8	1, 7	eqtri 2373	1 |- {A, B} = {x | (x = A \/ x = B)}

Syntax hints:   \/ wo 357   = wceq 1642   e. wcel 1710  {cab 2339   u. cun 3208  {csn 3738  {cpr 3739

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-v 2862  df-nin 3212  df-compl 3213  df-un 3215  df-sn 3742  df-pr 3743

This theorem is referenced by:  elprg  3751  nfpr  3774  pwpw0  3856  pwsn  3882  pwsnALT  3883