Constructor theory of probability.

Unitary quantum theory, having no Born Rule, is . Hence the notorious problem of reconciling it with the and in quantum measurements. Generalizing and improving upon the so-called 'decision-theoretic approach', I shall recast that problem in the recently proposed where quantum theory is represented as one of a class of , which are , theories conforming to certain constructor-theoretic conditions. I prove that the unpredictability of measurement outcomes (to which constructor theory gives an exact meaning) necessarily arises in superinformation theories. Then I explain how the appearance of stochasticity in (finitely many) repeated measurements can arise under superinformation theories. And I establish sufficient for a superinformation theory to inform decisions (made under it) it were probabilistic, via a Deutsch-Wallace-type argument-thus defining a class of superinformation theories. This broadens the domain of applicability of that argument to cover constructor-theory compliant theories. In addition, in this version some of the argument's assumptions, previously construed as merely decision-theoretic, follow from expressed by constructor-theoretic principles.