Given a unital C*-algebra A {\displaystyle {\mathcal {A}}} a *-closed subspace S containing 1 is called an operator system. One can to each to each subspace M ⊆ A {\displaystyle {\mathcal {M}}\subseteq {\mathcal {A}}} of an unital C*-algebra associate an operator system via S := M + M ∗ + C 1 {\displaystyle S:={\mathcal {M}}+{\mathcal {M}}^{*}+\mathbb {C} 1} .
