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Theorem dvdemo2 5248
 Description: Demonstration of a theorem that requires the setvar variables 𝑥 and 𝑧 to be disjoint (but without any other disjointness conditions, and in particular, none on 𝑦). That theorem bundles the theorems (⊢ ∃𝑥(𝑥 = 𝑦 → 𝑧 ∈ 𝑥) with 𝑥, 𝑦, 𝑧 disjoint), often called its "principal instance", and the two "degenerate instances" (⊢ ∃𝑥(𝑥 = 𝑥 → 𝑧 ∈ 𝑥) with 𝑥, 𝑧 disjoint) and (⊢ ∃𝑥(𝑥 = 𝑧 → 𝑧 ∈ 𝑥) with 𝑥, 𝑧 disjoint). Compare with dvdemo1 5247, which has the same principal instance and one common degenerate instance but crucially differs in the other degenerate instance. See https://us.metamath.org/mpeuni/mmset.html#distinct 5247 for details on the "disjoint variable" mechanism. Note that dvdemo2 5248 is partially bundled, in that the pairs of setvar variables 𝑥, 𝑦 and 𝑦, 𝑧 need not be disjoint, and in spite of that, its proof does not require any of the auxiliary axioms ax-10 2146, ax-11 2162, ax-12 2178, ax-13 2391. (Contributed by NM, 1-Dec-2006.) (Revised by BJ, 13-Jan-2024.)
Assertion
Ref Expression
dvdemo2 𝑥(𝑥 = 𝑦𝑧𝑥)
Distinct variable group:   𝑥,𝑧

Proof of Theorem dvdemo2
StepHypRef Expression
1 el 5243 . 2 𝑥 𝑧𝑥
2 ax-1 6 . 2 (𝑧𝑥 → (𝑥 = 𝑦𝑧𝑥))
31, 2eximii 1838 1 𝑥(𝑥 = 𝑦𝑧𝑥)
 Colors of variables: wff setvar class Syntax hints:   → wi 4  ∃wex 1781 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 1912  ax-6 1971  ax-7 2016  ax-8 2117  ax-9 2125  ax-pow 5239 This theorem depends on definitions:  df-bi 210  df-an 400  df-ex 1782 This theorem is referenced by: (None)
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