source 2007 Bernstein--Birkner--Lange--Peters parameter a3 assume a3 = 3 a assume Z1 = 1 assume Z2 = 1 compute C = X1-X2 compute D = 2(Y1-Y2) compute F = C^2 compute F4 = 4 F compute Z3 = 2 C compute G = C F4 compute H = X2 F4 compute X3 = D^2-G-2 H-a3 F4 compute Y3 = D(H-X3)-2 Y2 G compute ZZ3 = F4