Theorem rexss 3334

Description: Restricted existential quantification on a subset in terms of superset. (Contributed by Stefan O'Rear, 3-Apr-2015.)

Assertion

Ref	Expression
rexss	⊢ (A ⊆ B → (∃x ∈ A φ ↔ ∃x ∈ B (x ∈ A ∧ φ)))

Distinct variable groups:   x,A   x,B

Allowed substitution hint:   φ(x)

Proof of Theorem rexss

Step	Hyp	Ref	Expression
1		ssel 3268	. . . . 5 ⊢ (A ⊆ B → (x ∈ A → x ∈ B))
2	1	pm4.71rd 616	. . . 4 ⊢ (A ⊆ B → (x ∈ A ↔ (x ∈ B ∧ x ∈ A)))
3	2	anbi1d 685	. . 3 ⊢ (A ⊆ B → ((x ∈ A ∧ φ) ↔ ((x ∈ B ∧ x ∈ A) ∧ φ)))
4		anass 630	. . 3 ⊢ (((x ∈ B ∧ x ∈ A) ∧ φ) ↔ (x ∈ B ∧ (x ∈ A ∧ φ)))
5	3, 4	syl6bb 252	. 2 ⊢ (A ⊆ B → ((x ∈ A ∧ φ) ↔ (x ∈ B ∧ (x ∈ A ∧ φ))))
6	5	rexbidv2 2638	1 ⊢ (A ⊆ B → (∃x ∈ A φ ↔ ∃x ∈ B (x ∈ A ∧ φ)))

This proof depends on syntax axioms:   → wi 4   ↔ wb 176   ∧ wa 358   ∈ wcel 1710  ∃wrex 2616   ⊆ wss 3258

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This proof depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-rex 2621  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-ss 3260

This theorem is used by: (None)