Theorem tfsconcatrnsson

Description: The concatenation of transfinite sequences yields ordinals iff both sequences yield ordinals. Theorem 4 in Grzegorz Bancerek, "Epsilon Numbers and Cantor Normal Form", Formalized Mathematics, Vol. 17, No. 4, Pages 249–256, 2009. DOI: 10.2478/v10037-009-0032-8 (Contributed by RP, 2-Mar-2025)

	Ref	Expression
Hypothesis	tfsconcat.op	⊢ + = ( 𝑎 ∈ V , 𝑏 ∈ V ↦ ( 𝑎 ∪ { ⟨ 𝑥 , 𝑦 ⟩ ∣ ( 𝑥 ∈ ( ( dom 𝑎 +o dom 𝑏 ) ∖ dom 𝑎 ) ∧ ∃ 𝑧 ∈ dom 𝑏 ( 𝑥 = ( dom 𝑎 +o 𝑧 ) ∧ 𝑦 = ( 𝑏 ‘ 𝑧 ) ) ) } ) )
Assertion	tfsconcatrnsson	⊢ ( ( ( 𝐴 Fn 𝐶 ∧ 𝐵 Fn 𝐷 ) ∧ ( 𝐶 ∈ On ∧ 𝐷 ∈ On ) ) → ( ran ( 𝐴 + 𝐵 ) ⊆ On ↔ ( ran 𝐴 ⊆ On ∧ ran 𝐵 ⊆ On ) ) )

Proof

Step	Hyp	Ref	Expression
1		tfsconcat.op	⊢ + = ( 𝑎 ∈ V , 𝑏 ∈ V ↦ ( 𝑎 ∪ { ⟨ 𝑥 , 𝑦 ⟩ ∣ ( 𝑥 ∈ ( ( dom 𝑎 +o dom 𝑏 ) ∖ dom 𝑎 ) ∧ ∃ 𝑧 ∈ dom 𝑏 ( 𝑥 = ( dom 𝑎 +o 𝑧 ) ∧ 𝑦 = ( 𝑏 ‘ 𝑧 ) ) ) } ) )
2	1	tfsconcatrnss	⊢ ( ( ( 𝐴 Fn 𝐶 ∧ 𝐵 Fn 𝐷 ) ∧ ( 𝐶 ∈ On ∧ 𝐷 ∈ On ) ) → ( ran ( 𝐴 + 𝐵 ) ⊆ On ↔ ( ran 𝐴 ⊆ On ∧ ran 𝐵 ⊆ On ) ) )