Theorem bj-moeub 37516

Description: Uniqueness is equivalent to existence being equivalent to unique existence. (Contributed by BJ, 14-Oct-2022.)

Assertion

Ref	Expression
bj-moeub	⊢ (∃*𝑥𝜑 ↔ (∃𝑥𝜑 ↔ ∃!𝑥𝜑))

Proof of Theorem bj-moeub

Step	Hyp	Ref	Expression
1		moeu 2614	. 2 ⊢ (∃*𝑥𝜑 ↔ (∃𝑥𝜑 → ∃!𝑥𝜑))
2		euex 2608	. . . 4 ⊢ (∃!𝑥𝜑 → ∃𝑥𝜑)
3		impbi 211	. . . 4 ⊢ ((∃𝑥𝜑 → ∃!𝑥𝜑) → ((∃!𝑥𝜑 → ∃𝑥𝜑) → (∃𝑥𝜑 ↔ ∃!𝑥𝜑)))
4	2, 3	mpi 21	. . 3 ⊢ ((∃𝑥𝜑 → ∃!𝑥𝜑) → (∃𝑥𝜑 ↔ ∃!𝑥𝜑))
5		biimp 218	. . 3 ⊢ ((∃𝑥𝜑 ↔ ∃!𝑥𝜑) → (∃𝑥𝜑 → ∃!𝑥𝜑))
6	4, 5	impbii 212	. 2 ⊢ ((∃𝑥𝜑 → ∃!𝑥𝜑) ↔ (∃𝑥𝜑 ↔ ∃!𝑥𝜑))
7	1, 6	bitri 278	1 ⊢ (∃*𝑥𝜑 ↔ (∃𝑥𝜑 ↔ ∃!𝑥𝜑))

This proof depends on syntax axioms:   → wi 4   ↔ wb 209  ∃wex 1812  ∃*wmo 2568  ∃!weu 2599

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1828  ax-4 1842  ax-5 1943  ax-6 2000  ax-7 2041

This proof depends on definitions:  df-bi 210  df-an 402  df-ex 1813  df-mo 2570  df-eu 2600

This theorem is used by: (None)