Definition df-en 6707

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 6713. (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 6704	. 2 class ~~
2		vx	. . . . . 6 setvar x
3	2	cv 1342	. . . . 5 class x
4		vy	. . . . . 6 setvar y
5	4	cv 1342	. . . . 5 class y
6		vf	. . . . . 6 setvar f
7	6	cv 1342	. . . . 5 class f
8	3, 5, 7	wf1o 5187	. . . 4 wff f : x -1-1-onto-> y
9	8, 6	wex 1480	. . 3 wff E. f f : x -1-1-onto-> y
10	9, 2, 4	copab 4042	. 2 class { <. x , y >. | E. f f : x -1-1-onto-> y }
11	1, 10	wceq 1343	1 wff ~~ = { <. x , y >. | E. f f : x -1-1-onto-> y }

This definition is referenced by:  relen  6710  bren  6713  enssdom  6728