Metamath Proof Explorer
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 } ≈ 1o ) |
2 |
|
ensn1g |
⊢ ( 𝐵 ∈ 𝐷 → { 𝐵 } ≈ 1o ) |
3 |
2
|
ensymd |
⊢ ( 𝐵 ∈ 𝐷 → 1o ≈ { 𝐵 } ) |
4 |
|
entr |
⊢ ( ( { 𝐴 } ≈ 1o ∧ 1o ≈ { 𝐵 } ) → { 𝐴 } ≈ { 𝐵 } ) |
5 |
1 3 4
|
syl2an |
⊢ ( ( 𝐴 ∈ 𝐶 ∧ 𝐵 ∈ 𝐷 ) → { 𝐴 } ≈ { 𝐵 } ) |