if A is a infinite set ，define B={f|f is 1-1 correspondence on A}
I want to compute Card(B)
My attempt when A is finite ,then card(B)=$2^{card(A)}-2$
Such as A={$a_1,a_2$},then there exist two function f:$f(a_1)=a_2,f(a_2)=a_1$
$g:g(a_1)=a_1,g(a_2)=a_2$
So I guess when A is infinite ,card(B)=$2^{card(A)}$,but I can’t proof it can someone help me