Theorem enp1ilem 8746

Description: Lemma for uses of enp1i 8747. (Contributed by Mario Carneiro, 5-Jan-2016.)

Hypothesis

Ref	Expression
enp1ilem.1	⊢ 𝑇 = ({𝑥} ∪ 𝑆)

Assertion

Ref	Expression
enp1ilem	⊢ (𝑥 ∈ 𝐴 → ((𝐴 ∖ {𝑥}) = 𝑆 → 𝐴 = 𝑇))

Proof of Theorem enp1ilem

Step	Hyp	Ref	Expression
1		uneq1 4132	. . 3 ⊢ ((𝐴 ∖ {𝑥}) = 𝑆 → ((𝐴 ∖ {𝑥}) ∪ {𝑥}) = (𝑆 ∪ {𝑥}))
2		undif1 4424	. . 3 ⊢ ((𝐴 ∖ {𝑥}) ∪ {𝑥}) = (𝐴 ∪ {𝑥})
3		uncom 4129	. . . 4 ⊢ (𝑆 ∪ {𝑥}) = ({𝑥} ∪ 𝑆)
4		enp1ilem.1	. . . 4 ⊢ 𝑇 = ({𝑥} ∪ 𝑆)
5	3, 4	eqtr4i 2847	. . 3 ⊢ (𝑆 ∪ {𝑥}) = 𝑇
6	1, 2, 5	3eqtr3g 2879	. 2 ⊢ ((𝐴 ∖ {𝑥}) = 𝑆 → (𝐴 ∪ {𝑥}) = 𝑇)
7		snssi 4735	. . . 4 ⊢ (𝑥 ∈ 𝐴 → {𝑥} ⊆ 𝐴)
8		ssequn2 4159	. . . 4 ⊢ ({𝑥} ⊆ 𝐴 ↔ (𝐴 ∪ {𝑥}) = 𝐴)
9	7, 8	sylib 220	. . 3 ⊢ (𝑥 ∈ 𝐴 → (𝐴 ∪ {𝑥}) = 𝐴)
10	9	eqeq1d 2823	. 2 ⊢ (𝑥 ∈ 𝐴 → ((𝐴 ∪ {𝑥}) = 𝑇 ↔ 𝐴 = 𝑇))
11	6, 10	syl5ib 246	1 ⊢ (𝑥 ∈ 𝐴 → ((𝐴 ∖ {𝑥}) = 𝑆 → 𝐴 = 𝑇))

Syntax hints:   → wi 4   = wceq 1533   ∈ wcel 2110   ∖ cdif 3933   ∪ cun 3934   ⊆ wss 3936  {csn 4561

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-5 1907  ax-6 1966  ax-7 2011  ax-8 2112  ax-9 2120  ax-10 2141  ax-11 2156  ax-12 2172  ax-ext 2793

This theorem depends on definitions:  df-bi 209  df-an 399  df-or 844  df-3an 1085  df-tru 1536  df-ex 1777  df-nf 1781  df-sb 2066  df-clab 2800  df-cleq 2814  df-clel 2893  df-nfc 2963  df-rab 3147  df-v 3497  df-dif 3939  df-un 3941  df-in 3943  df-ss 3952  df-nul 4292  df-sn 4562

This theorem is referenced by:  en2  8748  en3  8749  en4  8750