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Theorem en1top 22838
Description: {∅} is the only topology with one element. (Contributed by FL, 18-Aug-2008.)
Assertion
Ref Expression
en1top (𝐽 ∈ Top → (𝐽 ≈ 1o𝐽 = {∅}))

Proof of Theorem en1top
StepHypRef Expression
1 0opn 22757 . . 3 (𝐽 ∈ Top → ∅ ∈ 𝐽)
2 en1eqsn 9273 . . . 4 ((∅ ∈ 𝐽𝐽 ≈ 1o) → 𝐽 = {∅})
32ex 412 . . 3 (∅ ∈ 𝐽 → (𝐽 ≈ 1o𝐽 = {∅}))
41, 3syl 17 . 2 (𝐽 ∈ Top → (𝐽 ≈ 1o𝐽 = {∅}))
5 id 22 . . 3 (𝐽 = {∅} → 𝐽 = {∅})
6 0ex 5300 . . . 4 ∅ ∈ V
76ensn1 9016 . . 3 {∅} ≈ 1o
85, 7eqbrtrdi 5180 . 2 (𝐽 = {∅} → 𝐽 ≈ 1o)
94, 8impbid1 224 1 (𝐽 ∈ Top → (𝐽 ≈ 1o𝐽 = {∅}))
Colors of variables: wff setvar class
Syntax hints:  wi 4  wb 205   = wceq 1533  wcel 2098  c0 4317  {csn 4623   class class class wbr 5141  1oc1o 8457  cen 8935  Topctop 22746
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1789  ax-4 1803  ax-5 1905  ax-6 1963  ax-7 2003  ax-8 2100  ax-9 2108  ax-10 2129  ax-11 2146  ax-12 2163  ax-ext 2697  ax-sep 5292  ax-nul 5299  ax-pr 5420
This theorem depends on definitions:  df-bi 206  df-an 396  df-or 845  df-3an 1086  df-tru 1536  df-fal 1546  df-ex 1774  df-nf 1778  df-sb 2060  df-mo 2528  df-eu 2557  df-clab 2704  df-cleq 2718  df-clel 2804  df-ne 2935  df-ral 3056  df-rex 3065  df-reu 3371  df-rab 3427  df-v 3470  df-dif 3946  df-un 3948  df-in 3950  df-ss 3960  df-nul 4318  df-if 4524  df-pw 4599  df-sn 4624  df-pr 4626  df-op 4630  df-uni 4903  df-br 5142  df-opab 5204  df-id 5567  df-xp 5675  df-rel 5676  df-cnv 5677  df-co 5678  df-dm 5679  df-rn 5680  df-res 5681  df-ima 5682  df-suc 6363  df-iota 6488  df-fun 6538  df-fn 6539  df-f 6540  df-f1 6541  df-fo 6542  df-f1o 6543  df-fv 6544  df-1o 8464  df-en 8939  df-top 22747
This theorem is referenced by:  hmph0  23650
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