let X be

set ;

for A being Subset of X holds ((0,1) --> (1,0)) * (chi ((A `),X)) = chi (A,X)let A be

Subset of

X;

((0,1) --> (1,0)) * (chi ((A `),X)) = chi (A,X)
(A `)

` = A
;

hence
((0,1)

--> (1,

0))

* (chi ((A `),X)) = chi (

A,

X)

by Th7;

verum