public static Either <Success, Error> Alternatively <Success, Error>
(this Either <Success, Error> initial, Func <Either <Success, Error> > subsequent) =>
initial.Unify(Either <Success, Error> .CreateSuccess, _ => subsequent());
public static Either <Success, Error> Alternatively <Success, Error>
(this Either <Success, Error> initial, Either <Success, Error> subsequent) =>
initial.Alternatively(() => subsequent);