“…For arbitrary partial strings, the refinement ordering ⊑ from Definition 3.5 is different from the containment of two pomset languages, cf. [7]. For example, the languages of the partial strings (a; b) (a; b) and N(a, a, b, b) -as shown in Figure 2 and 3, respectively -are contained in each other but (a; b) (a; b) N(a, a, b, b), see also Pratt [21,p.…”