MPE Home Metamath Proof Explorer < Previous   Next >
Nearby theorems
Mirrors  >  Home  >  MPE Home  >  Th. List  >  equvini Structured version   Visualization version   GIF version

Theorem equvini 2470
Description: A variable introduction law for equality. Lemma 15 of [Monk2] p. 109, however we do not require 𝑧 to be distinct from 𝑥 and 𝑦. Usage of this theorem is discouraged because it depends on ax-13 2383. See equvinv 2029 for a shorter proof requiring fewer axioms when 𝑧 is required to be distinct from 𝑥 and 𝑦. (Contributed by NM, 10-Jan-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.) (Proof shortened by Wolf Lammen, 16-Sep-2023.) (New usage is discouraged.)
Assertion
Ref Expression
equvini (𝑥 = 𝑦 → ∃𝑧(𝑥 = 𝑧𝑧 = 𝑦))

Proof of Theorem equvini
StepHypRef Expression
1 equtr 2021 . . . 4 (𝑧 = 𝑥 → (𝑥 = 𝑦𝑧 = 𝑦))
2 equcomi 2017 . . . 4 (𝑧 = 𝑥𝑥 = 𝑧)
31, 2jctild 528 . . 3 (𝑧 = 𝑥 → (𝑥 = 𝑦 → (𝑥 = 𝑧𝑧 = 𝑦)))
4 19.8a 2172 . . 3 ((𝑥 = 𝑧𝑧 = 𝑦) → ∃𝑧(𝑥 = 𝑧𝑧 = 𝑦))
53, 4syl6 35 . 2 (𝑧 = 𝑥 → (𝑥 = 𝑦 → ∃𝑧(𝑥 = 𝑧𝑧 = 𝑦)))
6 ax13 2386 . . 3 𝑧 = 𝑥 → (𝑥 = 𝑦 → ∀𝑧 𝑥 = 𝑦))
7 ax6e 2394 . . . . 5 𝑧 𝑧 = 𝑥
87, 3eximii 1830 . . . 4 𝑧(𝑥 = 𝑦 → (𝑥 = 𝑧𝑧 = 𝑦))
9819.35i 1872 . . 3 (∀𝑧 𝑥 = 𝑦 → ∃𝑧(𝑥 = 𝑧𝑧 = 𝑦))
106, 9syl6 35 . 2 𝑧 = 𝑥 → (𝑥 = 𝑦 → ∃𝑧(𝑥 = 𝑧𝑧 = 𝑦)))
115, 10pm2.61i 184 1 (𝑥 = 𝑦 → ∃𝑧(𝑥 = 𝑧𝑧 = 𝑦))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wa 398  wal 1528  wex 1773
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 1904  ax-6 1963  ax-7 2008  ax-12 2169  ax-13 2383
This theorem depends on definitions:  df-bi 209  df-an 399  df-ex 1774
This theorem is referenced by:  2ax6elem  2486
  Copyright terms: Public domain W3C validator