Theorem tfr1ALT

Description: Alternate proof of tfr1 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	tfr1ALT	|- F Fn On

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	wfr1	|- F Fn On