name W12 coordinates with a6=0
assume b = 0
variable X
variable Y
variable Z
neutral X = 1
neutral Y = 0
neutral Z = 0
satisfying ZZ = Z^2
satisfying x = X/Z
satisfying y = Y/ZZ
toaffine x = X/Z
toaffine y = Y/Z
tosystem X = x
tosystem Y = y
tosystem Z = 1
homogweight X = 1
homogweight Y = 2
homogweight Z = 1
