LAUSR

We prove the following characterization of the weak expectation property for operator systems in terms of an approximate version of Wittstock’s matricial Riesz separation property: an operator system S satisfies the weak expectation property if and only if $$M_{q}\left( S\right) $$MqS satisfies the approximate matricial Riesz separation property for every $$q\in \mathbb {N}$$q∈N. This can be seen as the noncommutative analog of the characterization of simplex spaces among function systems in terms of the classical Riesz separation property.