Random variables

independence
$X_1, X_2, ... ,X_n$ are mutually independent variables if and only if

$f(x_1,x_2,x_3,...,x_n)$ = $f_{X_1}(x_1) f_{X_2}(x_2$) ... $f_{X_n}(x_n) $

for all possible values of $x_1,x_2,x_3,...,x_n$