Viergruppe

The mathematical group $Z_2\otimes Z_2$, also denoted $D_2$. Its multiplication table is

$V$	$I$	$V_1$	$V_2$	$V_3$
$I$	$I$	$V_1$	$V_2$	$V_3$
$V_1$	$V_1$	$I$	$V_3$	$V_2$
$V_2$	$V_2$	$V_3$	$I$	$V_1$
$V_3$	$V_3$	$V_2$	$V_1$	$I$

See also Dihedral Group, Finite Group Z4