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
and then        , as proven in brcnv 4680
(see df-br 3894 and df-rel 4504 for more on relations). For example,
{ 2
, 6 , 3 , 9 } = { 6 , 2 ,
9 ,
3 } . 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.) |