Theorem difprsn1 3848

Description: Removal of a singleton from an unordered pair. (Contributed by Thierry Arnoux, 4-Feb-2017.)

Assertion

Ref	Expression
difprsn1	|- (A =/= B -> ({A, B} \ {A}) = {B})

Proof of Theorem difprsn1

Step	Hyp	Ref	Expression
1		necom 2598	. 2 |- (B =/= A <-> A =/= B)
2		disjsn2 3788	. . . 4 |- (B =/= A -> ({B} i^i {A}) = (/))
3		disj3 3596	. . . 4 |- (({B} i^i {A}) = (/) <-> {B} = ({B} \ {A}))
4	2, 3	sylib 188	. . 3 |- (B =/= A -> {B} = ({B} \ {A}))
5		df-pr 3743	. . . . . 6 |- {A, B} = ({A} u. {B})
6	5	equncomi 3411	. . . . 5 |- {A, B} = ({B} u. {A})
7	6	difeq1i 3382	. . . 4 |- ({A, B} \ {A}) = (({B} u. {A}) \ {A})
8		difun2 3630	. . . 4 |- (({B} u. {A}) \ {A}) = ({B} \ {A})
9	7, 8	eqtri 2373	. . 3 |- ({A, B} \ {A}) = ({B} \ {A})
10	4, 9	syl6reqr 2404	. 2 |- (B =/= A -> ({A, B} \ {A}) = {B})
11	1, 10	sylbir 204	1 |- (A =/= B -> ({A, B} \ {A}) = {B})

Syntax hints:   -> wi 4   = wceq 1642   =/= wne 2517   \ cdif 3207   u. cun 3208   i^i cin 3209  (/)c0 3551  {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-ne 2519  df-ral 2620  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-un 3215  df-dif 3216  df-ss 3260  df-nul 3552  df-sn 3742  df-pr 3743

This theorem is referenced by:  difprsn2  3849