Definition df-cnv 4921

Description: Define the converse of a class. Definition 9.12 of [Quine] p. 64. The converse of a binary relation swaps its arguments, i.e., if A e. _V and B e. _V then ( A `' R B <-> B R A ), as proven in brcnv 5098 (see df-br 4368 and df-rel 4920 for more on relations). For example, `' { <. 2 , 6 >. , <. 3 , 9 >. } = { <. 6 , 2 >. , <. 9 , 3 >. } (ex-cnv 25279). We use Quine's breve accent (smile) notation. Like Quine, we use it as a prefix, which eliminates the need for parentheses. Many authors use the postfix superscript "to the minus one." "Converse" is Quine's terminology; some authors call it "inverse," especially when the argument is a function. (Contributed by NM, 4-Jul-1994.)

Assertion

Ref	Expression
df-cnv	|- `' A = { <. x , y >. | y A x }

Distinct variable group:   x, y, A

Detailed syntax breakdown of Definition df-cnv

Step	Hyp	Ref	Expression
1		cA	. . 3 class A
2	1	ccnv 4912	. 2 class `' A
3		vy	. . . . 5 setvar y
4	3	cv 1398	. . . 4 class y
5		vx	. . . . 5 setvar x
6	5	cv 1398	. . . 4 class x
7	4, 6, 1	wbr 4367	. . 3 wff y A x
8	7, 5, 3	copab 4424	. 2 class { <. x , y >. | y A x }
9	2, 8	wceq 1399	1 wff `' A = { <. x , y >. | y A x }

This definition is referenced by:  cnvss  5088  elcnv  5092  nfcnv  5094  opelcnvg  5095  csbcnv  5099  csbcnvgALT  5100  cnvco  5101  relcnv  5287  cnvi  5320  cnvun  5321  cnvcnv3  5365