Theorem tfr2ALT

Description: Alternate proof of tfr2 using well-founded recursion. (Contributed by Scott Fenton, 3-Aug-2020) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Hypothesis	tfrALT.1	⊢ 𝐹 = recs ( 𝐺 )
Assertion	tfr2ALT	⊢ ( 𝐴 ∈ On → ( 𝐹 ‘ 𝐴 ) = ( 𝐺 ‘ ( 𝐹 ↾ 𝐴 ) ) )

Proof

Step	Hyp	Ref	Expression
1		tfrALT.1	⊢ 𝐹 = recs ( 𝐺 )
2		epweon	⊢ E We On
3		epse	⊢ E Se On
4		df-recs	⊢ recs ( 𝐺 ) = wrecs ( E , On , 𝐺 )
5	1 4	eqtri	⊢ 𝐹 = wrecs ( E , On , 𝐺 )
6	2 3 5	wfr2	⊢ ( 𝐴 ∈ On → ( 𝐹 ‘ 𝐴 ) = ( 𝐺 ‘ ( 𝐹 ↾ Pred ( E , On , 𝐴 ) ) ) )
7		predon	⊢ ( 𝐴 ∈ On → Pred ( E , On , 𝐴 ) = 𝐴 )
8	7	reseq2d	⊢ ( 𝐴 ∈ On → ( 𝐹 ↾ Pred ( E , On , 𝐴 ) ) = ( 𝐹 ↾ 𝐴 ) )
9	8	fveq2d	⊢ ( 𝐴 ∈ On → ( 𝐺 ‘ ( 𝐹 ↾ Pred ( E , On , 𝐴 ) ) ) = ( 𝐺 ‘ ( 𝐹 ↾ 𝐴 ) ) )
10	6 9	eqtrd	⊢ ( 𝐴 ∈ On → ( 𝐹 ‘ 𝐴 ) = ( 𝐺 ‘ ( 𝐹 ↾ 𝐴 ) ) )