Definition df-en 6909

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 6916. (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 6906	. 2 class ~~
2		vx	. . . . . 6 setvar x
3	2	cv 1396	. . . . 5 class x
4		vy	. . . . . 6 setvar y
5	4	cv 1396	. . . . 5 class y
6		vf	. . . . . 6 setvar f
7	6	cv 1396	. . . . 5 class f
8	3, 5, 7	wf1o 5325	. . . 4 wff f : x -1-1-onto-> y
9	8, 6	wex 1540	. . 3 wff E. f f : x -1-1-onto-> y
10	9, 2, 4	copab 4149	. 2 class { <. x , y >. | E. f f : x -1-1-onto-> y }
11	1, 10	wceq 1397	1 wff ~~ = { <. x , y >. | E. f f : x -1-1-onto-> y }

This definition is referenced by:  relen  6912  breng  6915  bren  6916  enssdom  6934