Definition df-en 7029

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 7036. (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 7026	. 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 5379	. . . 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 4192	. 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  7032  breng  7035  bren  7036  enssdom  7054