Concerning semirings of measurable functions

Abstract

For a measurable space $(X,\mathcal{A})$, let ${\mathcal{M}}^{+}(X,\mathcal{A})$ be the commutative semiring of non-negative real-valued measurable functions with pointwise addition and pointwise multiplication. We show that there is a lattice isomorphism between the ideal lattice of ${\mathcal{M}}^{+}(X,\mathcal{A})$ and the ideal lattice of its ring of differences $\mathcal{M}(X,\mathcal{A})$. Moreover, we infer that each ideal of ${\mathcal{M}}^{+}(X,\mathcal{A})$ is a semiring $z$-ideal. We investigate the duality between cancellative congruences on ${\mathcal{M}}^{+}(X,\mathcal{A})$ and $Z_{\mathcal{A}}$-filters on $X$. We observe that for $\sigma$-algebras, compactness and pseudocompactness coincide, and we provide a new characterization for compact measurable spaces via algebraic properties of ${\mathcal{M}}^{+}(X,\mathcal{A})$. It is shown that the space of (real) maximal congruences on ${\mathcal{M}}^{+}(X,\mathcal{A})$ is homeomorphic to the space of (real) maximal ideals of the $\mathcal{M}(X,\mathcal{A})$. We solve the isomorphism problem for the semirings of the form ${\mathcal{M}}^{+}(X,\mathcal{A})$ for compact and realcompact measurable spaces.