Definition df-en 6635

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 6641. (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 6632	. 2 class ~~
2		vx	. . . . . 6 setvar x
3	2	cv 1330	. . . . 5 class x
4		vy	. . . . . 6 setvar y
5	4	cv 1330	. . . . 5 class y
6		vf	. . . . . 6 setvar f
7	6	cv 1330	. . . . 5 class f
8	3, 5, 7	wf1o 5122	. . . 4 wff f : x -1-1-onto-> y
9	8, 6	wex 1468	. . 3 wff E. f f : x -1-1-onto-> y
10	9, 2, 4	copab 3988	. 2 class { <. x , y >. | E. f f : x -1-1-onto-> y }
11	1, 10	wceq 1331	1 wff ~~ = { <. x , y >. | E. f f : x -1-1-onto-> y }

This definition is referenced by:  relen  6638  bren  6641  enssdom  6656