>>12657520It probably isn't too different from the regular zeta.
Write s = |s|*q where q is a versor.
https://en.wikipedia.org/wiki/Versorq = exp(a*r) = cos(a) + r*sin(a) where r is a unit length vector quaternion (r^2 = -1).
s = |s|*cos(a) + r*|s|*sin(a).
Since r behaves like i, evaluating at s is equivalent to evaluating at x+iy where x=|s|cos(a) and y = |s|sin(a) then replacing the i in the output by r.
Basically there is no change in how to evaluate zeta at a quaternion from how to evaluate it at a complex number.
