background and aims. gingival recession (gr), a common problem in periodontium, is associated with various etiologic factors. there is controversy over the role and importance of these factors. the aim of this study was to evaluate the etiologic factors of gr in a group of subjects in northwest iran. materials and methods. in this case-control study, patients referring to a university clinic (1...

Corresponding reduction (cut-elimination) rules are added, which express operationally this new !/? symmetry. These reduction rules are semantically justified, when interpreting the new logical rules for “!” as standard operations on functions (in particular, codereliction corresponds to differentiation of a function at point 0 of a vector space). This extended linear logic is called Differenti...