Theorem iota0ndef 43281

Description: Example for an undefined iota being the empty set, i.e., ∀𝑦𝑦 ∈ 𝑥 is a wff not satisfied by a (unique) value 𝑥 (there is no set, and therefore certainly no unique set, which contains every set). (Contributed by AV, 24-Aug-2022.)

Assertion

Ref	Expression
iota0ndef	⊢ (℩𝑥∀𝑦 𝑦 ∈ 𝑥) = ∅

Distinct variable group:   𝑥,𝑦

Proof of Theorem iota0ndef

Step	Hyp	Ref	Expression
1		nalset 5219	. . . 4 ⊢ ¬ ∃𝑥∀𝑦 𝑦 ∈ 𝑥
2	1	intnanr 490	. . 3 ⊢ ¬ (∃𝑥∀𝑦 𝑦 ∈ 𝑥 ∧ ∃*𝑥∀𝑦 𝑦 ∈ 𝑥)
3		df-eu 2654	. . 3 ⊢ (∃!𝑥∀𝑦 𝑦 ∈ 𝑥 ↔ (∃𝑥∀𝑦 𝑦 ∈ 𝑥 ∧ ∃*𝑥∀𝑦 𝑦 ∈ 𝑥))
4	2, 3	mtbir 325	. 2 ⊢ ¬ ∃!𝑥∀𝑦 𝑦 ∈ 𝑥
5		iotanul 6335	. 2 ⊢ (¬ ∃!𝑥∀𝑦 𝑦 ∈ 𝑥 → (℩𝑥∀𝑦 𝑦 ∈ 𝑥) = ∅)
6	4, 5	ax-mp 5	1 ⊢ (℩𝑥∀𝑦 𝑦 ∈ 𝑥) = ∅

Syntax hints:  ¬ wn 3   ∧ wa 398  ∀wal 1535   = wceq 1537  ∃wex 1780  ∃*wmo 2620  ∃!weu 2653  ∅c0 4293  ℩cio 6314

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1796  ax-4 1810  ax-5 1911  ax-6 1970  ax-7 2015  ax-8 2116  ax-9 2124  ax-10 2145  ax-11 2161  ax-12 2177  ax-ext 2795  ax-sep 5205

This theorem depends on definitions:  df-bi 209  df-an 399  df-or 844  df-tru 1540  df-ex 1781  df-nf 1785  df-sb 2070  df-mo 2622  df-eu 2654  df-clab 2802  df-cleq 2816  df-clel 2895  df-nfc 2965  df-ral 3145  df-rex 3146  df-v 3498  df-dif 3941  df-in 3945  df-ss 3954  df-nul 4294  df-sn 4570  df-uni 4841  df-iota 6316

This theorem is referenced by: (None)