Morita equivalence for operator systems.

We define $\Delta$-equivalence for operator systems and show that it is identical to stable isomorphism. We define $\Delta$-contexts and bihomomorphism contexts and show that two operator systems are $\Delta$-equivalent if and only if they can be placed in a $\Delta$-context, equivalently, in a bihomomorphism context. We show that nuclearity for a variety of tensor products is an invariant for $\Delta$-equivalence and that function systems are $\Delta$-equivalent precisely when they are order isomorphic. We prove that $\Delta$-equivalent operator systems have equivalent categories of representations. As an application, we characterise $\Delta$-equivalence of graph operator systems in combinatorial terms.