A cura di: Alfredo Bochicchio

$[(1/2x+2/3y+z)^2-(1/2+2/3y-z)^2+1/3yz]^2-3yz^2(4x+3y)$
$[1/4x^2+4/9y^2+z^2+2/3xy+xz+4/3yz-1/2x^2-4/9y^2-z^2-2/3xy+xz+4/3yz+1/3yz]^2-12xyz^2-9y^2z^2$
$[2xz+3yz]^2-12xyz^2-9y^2z^2$
$4x^2z^2+12xyz^2+9y^2z^2-9y^2z^2-12xyz^2$
$rx^2z^2$