The concept of a relatively weakly injective pair of operator systems is introduced and studied in this paper, motivated by relative weak injectivity in the C*-algebra category. E. Kirchberg \cite{ Kr} proved that the C*-algebra $C^*(\mathbb{ f}_\infty)$ of the free group $\mathbb{ f}_\infty$ on countably many generators characterizes relative weak injectivity for pairs of C*-algebras by means of the maximal tensor product. One of the main results of this paper shows that $C^*(\mathbb{ f}_\infty)$ also characterises relative weak injectivity in the operator system category. A key tool is the theory of operator system tensor products \cite{ KP1,KP2}.
Categories: math.OA