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Theorem fr0 5502
 Description: Any relation is well-founded on the empty set. (Contributed by NM, 17-Sep-1993.)
Assertion
Ref Expression
fr0 𝑅 Fr ∅

Proof of Theorem fr0
Dummy variables 𝑥 𝑦 𝑧 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 dffr2 5488 . 2 (𝑅 Fr ∅ ↔ ∀𝑥((𝑥 ⊆ ∅ ∧ 𝑥 ≠ ∅) → ∃𝑦𝑥 {𝑧𝑥𝑧𝑅𝑦} = ∅))
2 ss0 4309 . . . . 5 (𝑥 ⊆ ∅ → 𝑥 = ∅)
32a1d 25 . . . 4 (𝑥 ⊆ ∅ → (¬ ∃𝑦𝑥 {𝑧𝑥𝑧𝑅𝑦} = ∅ → 𝑥 = ∅))
43necon1ad 3007 . . 3 (𝑥 ⊆ ∅ → (𝑥 ≠ ∅ → ∃𝑦𝑥 {𝑧𝑥𝑧𝑅𝑦} = ∅))
54imp 410 . 2 ((𝑥 ⊆ ∅ ∧ 𝑥 ≠ ∅) → ∃𝑦𝑥 {𝑧𝑥𝑧𝑅𝑦} = ∅)
61, 5mpgbir 1801 1 𝑅 Fr ∅
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 399   = wceq 1538   ≠ wne 2990  ∃wrex 3110  {crab 3113   ⊆ wss 3884  ∅c0 4246   class class class wbr 5033   Fr wfr 5479 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1911  ax-6 1970  ax-7 2015  ax-8 2114  ax-9 2122  ax-10 2143  ax-11 2159  ax-12 2176  ax-ext 2773 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-tru 1541  df-ex 1782  df-nf 1786  df-sb 2070  df-clab 2780  df-cleq 2794  df-clel 2873  df-nfc 2941  df-ne 2991  df-ral 3114  df-rex 3115  df-rab 3118  df-v 3446  df-dif 3887  df-in 3891  df-ss 3901  df-nul 4247  df-fr 5482 This theorem is referenced by:  we0  5518  frsn  5607  frfi  8751  ifr0  41141
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