Database
ZF (ZERMELO-FRAENKEL) SET THEORY
ZF Set Theory - add the Axiom of Union
Equinumerosity
en2sn
Next ⟩
snfi
Metamath Proof Explorer
Ascii
Unicode
Theorem
en2sn
Description:
Two singletons are equinumerous.
(Contributed by
NM
, 9-Nov-2003)
Ref
Expression
Assertion
en2sn
⊢
A
∈
C
∧
B
∈
D
→
A
≈
B
Proof
Step
Hyp
Ref
Expression
1
ensn1g
⊢
A
∈
C
→
A
≈
1
𝑜
2
ensn1g
⊢
B
∈
D
→
B
≈
1
𝑜
3
2
ensymd
⊢
B
∈
D
→
1
𝑜
≈
B
4
entr
⊢
A
≈
1
𝑜
∧
1
𝑜
≈
B
→
A
≈
B
5
1
3
4
syl2an
⊢
A
∈
C
∧
B
∈
D
→
A
≈
B