A2 critical coordinates: Z = -X - Y
curve relation: X^2 + X*Y + Y^2 = g2/4
V2 = sum wp'' = 3*g2/2
Hessian = 2*n*n^T, n = (2*X+Y, X+2*Y)
s^2 = 4*X*Y*Z - g3
first normal equation: n dot xi = s/2
effective e2^2 term = V4/360 - s^2/4 = 3*g3/20
all exact polynomial identities passed