Theorem eqsn 3868

Description: Two ways to express that a nonempty set equals a singleton. (Contributed by NM, 15-Dec-2007.)

Assertion

Ref	Expression
eqsn	|- (A =/= (/) -> (A = {B} <-> A.x e. A x = B))

Distinct variable groups:   x,A   x,B

Proof of Theorem eqsn

Step	Hyp	Ref	Expression
1		eqimss 3324	. . 3 |- (A = {B} -> A C_ {B})
2		df-ne 2519	. . . . 5 |- (A =/= (/) <-> -. A = (/))
3		sssn 3865	. . . . . . 7 |- (A C_ {B} <-> (A = (/) \/ A = {B}))
4	3	biimpi 186	. . . . . 6 |- (A C_ {B} -> (A = (/) \/ A = {B}))
5	4	ord 366	. . . . 5 |- (A C_ {B} -> (-. A = (/) -> A = {B}))
6	2, 5	syl5bi 208	. . . 4 |- (A C_ {B} -> (A =/= (/) -> A = {B}))
7	6	com12 27	. . 3 |- (A =/= (/) -> (A C_ {B} -> A = {B}))
8	1, 7	impbid2 195	. 2 |- (A =/= (/) -> (A = {B} <-> A C_ {B}))
9		dfss3 3264	. . 3 |- (A C_ {B} <-> A.x e. A x e. {B})
10		elsn 3749	. . . 4 |- (x e. {B} <-> x = B)
11	10	ralbii 2639	. . 3 |- (A.x e. A x e. {B} <-> A.x e. A x = B)
12	9, 11	bitri 240	. 2 |- (A C_ {B} <-> A.x e. A x = B)
13	8, 12	syl6bb 252	1 |- (A =/= (/) -> (A = {B} <-> A.x e. A x = B))

Syntax hints:  -. wn 3   -> wi 4   <-> wb 176   \/ wo 357   = wceq 1642   e. wcel 1710   =/= wne 2517  A.wral 2615   C_ wss 3258  (/)c0 3551  {csn 3738

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-ne 2519  df-ral 2620  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-dif 3216  df-ss 3260  df-nul 3552  df-sn 3742

This theorem is referenced by: (None)