source 1998 Cohen--Miyaji--Ono "Efficient elliptic curve exponentiation using mixed coordinates", formula (4)
compute w = a Z1^2+3 X1^2
compute s = Y1 Z1
compute B = X1 Y1 s
compute h = w^2-8 B
compute X3 = 2 h s
compute Y3 = w(4 B-h)-8 Y1^2 s^2
compute Z3 = 8 s^3
