We show that every state on an interval effect algebra is an integral through some regular Borel probability measure defined on the Borel $\sigma$-algebra of a compact Hausdorff simplex. This is true for every effect algebra satisfying (RDP) or for every MV-algebra. In addition, we show that each state on an effect subalgebra of an interval effect algebra $E$ can be extended to a state on $E.$ Our method represents also every state on the set of effect operators of a Hilbert space as an integral
Categories: math.FA