Database
ZF (ZERMELO-FRAENKEL) SET THEORY
ZF Set Theory - add the Axiom of Union
Finite sets
infn0
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fin2inf
Metamath Proof Explorer
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Unicode
Theorem
infn0
Description:
An infinite set is not empty.
(Contributed by
NM
, 23-Oct-2004)
Ref
Expression
Assertion
infn0
⊢
ω
≼
A
→
A
≠
∅
Proof
Step
Hyp
Ref
Expression
1
peano1
⊢
∅
∈
ω
2
infsdomnn
⊢
ω
≼
A
∧
∅
∈
ω
→
∅
≺
A
3
1
2
mpan2
⊢
ω
≼
A
→
∅
≺
A
4
reldom
⊢
Rel
⁡
≼
5
4
brrelex2i
⊢
ω
≼
A
→
A
∈
V
6
0sdomg
⊢
A
∈
V
→
∅
≺
A
↔
A
≠
∅
7
5
6
syl
⊢
ω
≼
A
→
∅
≺
A
↔
A
≠
∅
8
3
7
mpbid
⊢
ω
≼
A
→
A
≠
∅