# What is the sequence type if ROC is an annulus in the z-plane

if:

$$|z|>|\alpha|$$ is causal and right-sided

and:

$$|z|<|\alpha|$$ is anti-causal and left-sided

then, what is the annulus/donut-ring ROC?

$$|\beta| < |z| < |\alpha|$$

non-casual? finite-length? double-sided?