name projective coordinates
variable X
variable Y
variable Z
neutral X = 0
neutral Y = c
neutral Z = 1
satisfying x = X/Z
satisfying y = Y/Z
toaffine x = X/Z
toaffine y = Y/Z
tosystem X = x
tosystem Y = y
tosystem Z = 1
homogweight X = 1
homogweight Y = 1
homogweight Z = 1
