A = Y2-Y1
AA = A^2
B = X2-X1
CC = B^2
F = X1*CC
Z3 = 2*CC
D = X2*Z3
ZZ3 = Z3^2
t0 = AA-F
t1 = a*Z3
t2 = 2*t0
t3 = t2-t1
X3 = t3-D
t4 = A+B
t5 = t4^2
t6 = t5-AA
t7 = t6-CC
t8 = D-X3
t9 = Y2*ZZ3
t10 = t7*t8
Y3 = t10-t9