Definition df-hf

Description: Define the hereditarily finite sets. These are the finite sets whose elements are finite, and so forth. (Contributed by Scott Fenton, 9-Jul-2015)

	Ref	Expression
Assertion	df-hf	|- Hf = U. ( R1 " _om )

Detailed syntax breakdown

Step	Hyp	Ref	Expression
0		chf	|- Hf
1		cr1	|- R1
2		com	|- _om
3	1 2	cima	|- ( R1 " _om )
4	3	cuni	|- U. ( R1 " _om )
5	0 4	wceq	|- Hf = U. ( R1 " _om )