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Theorem bj-sbsb 32520
 Description: Biconditional showing two possible (dual) definitions of substitution df-sb 1878 not using dummy variables. (Contributed by BJ, 19-Mar-2021.)
Assertion
Ref Expression
bj-sbsb (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) ↔ (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)))

Proof of Theorem bj-sbsb
StepHypRef Expression
1 simpl 473 . . . 4 (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) → (𝑥 = 𝑦𝜑))
2 pm2.27 42 . . . . . 6 (𝑥 = 𝑦 → ((𝑥 = 𝑦𝜑) → 𝜑))
32anc2li 579 . . . . 5 (𝑥 = 𝑦 → ((𝑥 = 𝑦𝜑) → (𝑥 = 𝑦𝜑)))
43sps 2053 . . . 4 (∀𝑥 𝑥 = 𝑦 → ((𝑥 = 𝑦𝜑) → (𝑥 = 𝑦𝜑)))
5 olc 399 . . . 4 ((𝑥 = 𝑦𝜑) → (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)))
61, 4, 5syl56 36 . . 3 (∀𝑥 𝑥 = 𝑦 → (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) → (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑))))
7 simpr 477 . . . 4 (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) → ∃𝑥(𝑥 = 𝑦𝜑))
8 equs5 2350 . . . . 5 (¬ ∀𝑥 𝑥 = 𝑦 → (∃𝑥(𝑥 = 𝑦𝜑) ↔ ∀𝑥(𝑥 = 𝑦𝜑)))
98biimpd 219 . . . 4 (¬ ∀𝑥 𝑥 = 𝑦 → (∃𝑥(𝑥 = 𝑦𝜑) → ∀𝑥(𝑥 = 𝑦𝜑)))
10 orc 400 . . . 4 (∀𝑥(𝑥 = 𝑦𝜑) → (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)))
117, 9, 10syl56 36 . . 3 (¬ ∀𝑥 𝑥 = 𝑦 → (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) → (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑))))
126, 11pm2.61i 176 . 2 (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) → (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)))
13 sp 2051 . . . 4 (∀𝑥(𝑥 = 𝑦𝜑) → (𝑥 = 𝑦𝜑))
14 pm3.4 583 . . . 4 ((𝑥 = 𝑦𝜑) → (𝑥 = 𝑦𝜑))
1513, 14jaoi 394 . . 3 ((∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)) → (𝑥 = 𝑦𝜑))
16 equs4 2289 . . . 4 (∀𝑥(𝑥 = 𝑦𝜑) → ∃𝑥(𝑥 = 𝑦𝜑))
17 19.8a 2049 . . . 4 ((𝑥 = 𝑦𝜑) → ∃𝑥(𝑥 = 𝑦𝜑))
1816, 17jaoi 394 . . 3 ((∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)) → ∃𝑥(𝑥 = 𝑦𝜑))
1915, 18jca 554 . 2 ((∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)) → ((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)))
2012, 19impbii 199 1 (((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)) ↔ (∀𝑥(𝑥 = 𝑦𝜑) ∨ (𝑥 = 𝑦𝜑)))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 196   ∨ wo 383   ∧ wa 384  ∀wal 1478  ∃wex 1701 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1719  ax-4 1734  ax-5 1836  ax-6 1885  ax-7 1932  ax-10 2016  ax-12 2044  ax-13 2245 This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-ex 1702  df-nf 1707 This theorem is referenced by:  bj-dfsb2  32521
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