Database
ZF (ZERMELO-FRAENKEL) SET THEORY
ZF Set Theory - start with the Axiom of Extensionality
The empty set
ralidm
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ral0
Metamath Proof Explorer
Ascii
Unicode
Theorem
ralidm
Description:
Idempotent law for restricted quantifier.
(Contributed by
NM
, 28-Mar-1997)
Ref
Expression
Assertion
ralidm
⊢
∀
x
∈
A
∀
x
∈
A
φ
↔
∀
x
∈
A
φ
Proof
Step
Hyp
Ref
Expression
1
rzal
⊢
A
=
∅
→
∀
x
∈
A
∀
x
∈
A
φ
2
rzal
⊢
A
=
∅
→
∀
x
∈
A
φ
3
1
2
2thd
⊢
A
=
∅
→
∀
x
∈
A
∀
x
∈
A
φ
↔
∀
x
∈
A
φ
4
neq0
⊢
¬
A
=
∅
↔
∃
x
x
∈
A
5
biimt
⊢
∃
x
x
∈
A
→
∀
x
∈
A
φ
↔
∃
x
x
∈
A
→
∀
x
∈
A
φ
6
df-ral
⊢
∀
x
∈
A
∀
x
∈
A
φ
↔
∀
x
x
∈
A
→
∀
x
∈
A
φ
7
nfra1
⊢
Ⅎ
x
∀
x
∈
A
φ
8
7
19.23
⊢
∀
x
x
∈
A
→
∀
x
∈
A
φ
↔
∃
x
x
∈
A
→
∀
x
∈
A
φ
9
6
8
bitri
⊢
∀
x
∈
A
∀
x
∈
A
φ
↔
∃
x
x
∈
A
→
∀
x
∈
A
φ
10
5
9
syl6rbbr
⊢
∃
x
x
∈
A
→
∀
x
∈
A
∀
x
∈
A
φ
↔
∀
x
∈
A
φ
11
4
10
sylbi
⊢
¬
A
=
∅
→
∀
x
∈
A
∀
x
∈
A
φ
↔
∀
x
∈
A
φ
12
3
11
pm2.61i
⊢
∀
x
∈
A
∀
x
∈
A
φ
↔
∀
x
∈
A
φ