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 (see df-br and df-rel for more on relations). For example,
``' { <. 2 , 6 >. , <. 3 , 9 >. } = { <. 6 , 2 >. , <. 9 , 3 >. } `
( ex-cnv ). 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 "minus one". The term
"converse" is Quine's terminology; some authors call it "inverse",
especially when the argument is a function. (Contributed by NM, 4-Jul-1994)