Theorem csbnestg

Description: Nest the composition of two substitutions. Usage of this theorem is discouraged because it depends on ax-13 . Use the weaker csbnestgw when possible. (Contributed by NM, 23-Nov-2005) (Proof shortened by Mario Carneiro, 10-Nov-2016) (New usage is discouraged.)

	Ref	Expression
Assertion	csbnestg	⊢ ( 𝐴 ∈ 𝑉 → ⦋ 𝐴 / 𝑥 ⦌ ⦋ 𝐵 / 𝑦 ⦌ 𝐶 = ⦋ ⦋ 𝐴 / 𝑥 ⦌ 𝐵 / 𝑦 ⦌ 𝐶 )

Proof

Step	Hyp	Ref	Expression
1		nfcv	⊢ Ⅎ 𝑥 𝐶
2	1	ax-gen	⊢ ∀ 𝑦 Ⅎ 𝑥 𝐶
3		csbnestgf	⊢ ( ( 𝐴 ∈ 𝑉 ∧ ∀ 𝑦 Ⅎ 𝑥 𝐶 ) → ⦋ 𝐴 / 𝑥 ⦌ ⦋ 𝐵 / 𝑦 ⦌ 𝐶 = ⦋ ⦋ 𝐴 / 𝑥 ⦌ 𝐵 / 𝑦 ⦌ 𝐶 )
4	2 3	mpan2	⊢ ( 𝐴 ∈ 𝑉 → ⦋ 𝐴 / 𝑥 ⦌ ⦋ 𝐵 / 𝑦 ⦌ 𝐶 = ⦋ ⦋ 𝐴 / 𝑥 ⦌ 𝐵 / 𝑦 ⦌ 𝐶 )