Definition df-en 7023

Description: Define the equinumerosity relation. Definition of [Enderton] p. 129. We define ~~ to be a binary relation rather than a connective, so its arguments must be sets to be meaningful. This is acceptable because we do not consider equinumerosity for proper classes. We derive the usual definition as bren 7030. (Contributed by NM, 28-Mar-1998.)

Assertion

Ref	Expression
df-en	|- ~~ = { <. x , y >. | E. f f : x -1-1-onto-> y }

Distinct variable group:   x, y, f

Detailed syntax breakdown of Definition df-en

Step	Hyp	Ref	Expression
1		cen 7020	. 2 class ~~
2		vx	. . . . . 6 setvar x
3	2	cv 1401	. . . . 5 class x
4		vy	. . . . . 6 setvar y
5	4	cv 1401	. . . . 5 class y
6		vf	. . . . . 6 setvar f
7	6	cv 1401	. . . . 5 class f
8	3, 5, 7	wf1o 5376	. . . 4 wff f : x -1-1-onto-> y
9	8, 6	wex 1545	. . 3 wff E. f f : x -1-1-onto-> y
10	9, 2, 4	copab 4191	. 2 class { <. x , y >. | E. f f : x -1-1-onto-> y }
11	1, 10	wceq 1402	1 wff ~~ = { <. x , y >. | E. f f : x -1-1-onto-> y }

This definition is used by:  relen  7026  breng  7029  bren  7030  enssdom  7048