Theorem 19.30dc 1607

Description: Theorem 19.30 of [Margaris] p. 90, with an additional decidability condition. (Contributed by Jim Kingdon, 21-Jul-2018.)

Assertion

Ref	Expression
19.30dc	⊢ (DECID ∃𝑥𝜓 → (∀𝑥(𝜑 ∨ 𝜓) → (∀𝑥𝜑 ∨ ∃𝑥𝜓)))

Proof of Theorem 19.30dc

Step	Hyp	Ref	Expression
1		df-dc 821	. 2 ⊢ (DECID ∃𝑥𝜓 ↔ (∃𝑥𝜓 ∨ ¬ ∃𝑥𝜓))
2		olc 701	. . . 4 ⊢ (∃𝑥𝜓 → (∀𝑥𝜑 ∨ ∃𝑥𝜓))
3	2	a1d 22	. . 3 ⊢ (∃𝑥𝜓 → (∀𝑥(𝜑 ∨ 𝜓) → (∀𝑥𝜑 ∨ ∃𝑥𝜓)))
4		alnex 1476	. . . . 5 ⊢ (∀𝑥 ¬ 𝜓 ↔ ¬ ∃𝑥𝜓)
5		orel2 716	. . . . . 6 ⊢ (¬ 𝜓 → ((𝜑 ∨ 𝜓) → 𝜑))
6	5	al2imi 1435	. . . . 5 ⊢ (∀𝑥 ¬ 𝜓 → (∀𝑥(𝜑 ∨ 𝜓) → ∀𝑥𝜑))
7	4, 6	sylbir 134	. . . 4 ⊢ (¬ ∃𝑥𝜓 → (∀𝑥(𝜑 ∨ 𝜓) → ∀𝑥𝜑))
8		orc 702	. . . 4 ⊢ (∀𝑥𝜑 → (∀𝑥𝜑 ∨ ∃𝑥𝜓))
9	7, 8	syl6 33	. . 3 ⊢ (¬ ∃𝑥𝜓 → (∀𝑥(𝜑 ∨ 𝜓) → (∀𝑥𝜑 ∨ ∃𝑥𝜓)))
10	3, 9	jaoi 706	. 2 ⊢ ((∃𝑥𝜓 ∨ ¬ ∃𝑥𝜓) → (∀𝑥(𝜑 ∨ 𝜓) → (∀𝑥𝜑 ∨ ∃𝑥𝜓)))
11	1, 10	sylbi 120	1 ⊢ (DECID ∃𝑥𝜓 → (∀𝑥(𝜑 ∨ 𝜓) → (∀𝑥𝜑 ∨ ∃𝑥𝜓)))

Syntax hints:  ¬ wn 3   → wi 4   ∨ wo 698  DECID wdc 820  ∀wal 1330  ∃wex 1469

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605  ax-io 699  ax-5 1424  ax-gen 1426  ax-ie2 1471

This theorem depends on definitions:  df-bi 116  df-dc 821  df-tru 1335  df-fal 1338

This theorem is referenced by: (None)