Metamath Proof Explorer


Theorem newbday

Description: A surreal is an element of a new set iff its birthday is equal to that ordinal. Remark in Conway p. 29. (Contributed by Scott Fenton, 19-Aug-2024)

Ref Expression
Assertion newbday ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( 𝑋 ∈ ( N ‘ 𝐴 ) ↔ ( bday 𝑋 ) = 𝐴 ) )

Proof

Step Hyp Ref Expression
1 madebday ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( 𝑋 ∈ ( M ‘ 𝐴 ) ↔ ( bday 𝑋 ) ⊆ 𝐴 ) )
2 oldbday ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( 𝑋 ∈ ( O ‘ 𝐴 ) ↔ ( bday 𝑋 ) ∈ 𝐴 ) )
3 2 notbid ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( ¬ 𝑋 ∈ ( O ‘ 𝐴 ) ↔ ¬ ( bday 𝑋 ) ∈ 𝐴 ) )
4 1 3 anbi12d ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( ( 𝑋 ∈ ( M ‘ 𝐴 ) ∧ ¬ 𝑋 ∈ ( O ‘ 𝐴 ) ) ↔ ( ( bday 𝑋 ) ⊆ 𝐴 ∧ ¬ ( bday 𝑋 ) ∈ 𝐴 ) ) )
5 newval ( N ‘ 𝐴 ) = ( ( M ‘ 𝐴 ) ∖ ( O ‘ 𝐴 ) )
6 5 a1i ( 𝐴 ∈ On → ( N ‘ 𝐴 ) = ( ( M ‘ 𝐴 ) ∖ ( O ‘ 𝐴 ) ) )
7 6 eleq2d ( 𝐴 ∈ On → ( 𝑋 ∈ ( N ‘ 𝐴 ) ↔ 𝑋 ∈ ( ( M ‘ 𝐴 ) ∖ ( O ‘ 𝐴 ) ) ) )
8 eldif ( 𝑋 ∈ ( ( M ‘ 𝐴 ) ∖ ( O ‘ 𝐴 ) ) ↔ ( 𝑋 ∈ ( M ‘ 𝐴 ) ∧ ¬ 𝑋 ∈ ( O ‘ 𝐴 ) ) )
9 7 8 bitrdi ( 𝐴 ∈ On → ( 𝑋 ∈ ( N ‘ 𝐴 ) ↔ ( 𝑋 ∈ ( M ‘ 𝐴 ) ∧ ¬ 𝑋 ∈ ( O ‘ 𝐴 ) ) ) )
10 9 adantr ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( 𝑋 ∈ ( N ‘ 𝐴 ) ↔ ( 𝑋 ∈ ( M ‘ 𝐴 ) ∧ ¬ 𝑋 ∈ ( O ‘ 𝐴 ) ) ) )
11 bdayelon ( bday 𝑋 ) ∈ On
12 11 onordi Ord ( bday 𝑋 )
13 eloni ( 𝐴 ∈ On → Ord 𝐴 )
14 ordtri4 ( ( Ord ( bday 𝑋 ) ∧ Ord 𝐴 ) → ( ( bday 𝑋 ) = 𝐴 ↔ ( ( bday 𝑋 ) ⊆ 𝐴 ∧ ¬ ( bday 𝑋 ) ∈ 𝐴 ) ) )
15 12 13 14 sylancr ( 𝐴 ∈ On → ( ( bday 𝑋 ) = 𝐴 ↔ ( ( bday 𝑋 ) ⊆ 𝐴 ∧ ¬ ( bday 𝑋 ) ∈ 𝐴 ) ) )
16 15 adantr ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( ( bday 𝑋 ) = 𝐴 ↔ ( ( bday 𝑋 ) ⊆ 𝐴 ∧ ¬ ( bday 𝑋 ) ∈ 𝐴 ) ) )
17 4 10 16 3bitr4d ( ( 𝐴 ∈ On ∧ 𝑋 No ) → ( 𝑋 ∈ ( N ‘ 𝐴 ) ↔ ( bday 𝑋 ) = 𝐴 ) )