(SI) Glavni cilji bilateralnega sodelovanja so: (1) Natančno analizirati pogoje, pod katerimi so pripadajoči digrafi HAT grafov stopnje 4 stopničasti. (2) Natančno analizirati in po možnosti klasificirati tiste HAT grafe stopnje 4 s stopničastimi pripadajočimi digrafi, pri katerih je vsak nivo unija množice repov dveh alternirajočih ciklov (in obenem unija množice glav dveh alternirajočih ciklov). (3) Natančno analizirati in po možnosti klasificirati tiste HAT grafe stopnje 4 s stopničastimi pripadajočimi digrafi, za katere je podgrupa avtomorfizmov, ki ohranja vse nivoje, komutativna.
(EN) The main objectives of the bilateral cooperation are: (1) To analyze in detail the conditions under which the associated digraphs of the HAT graphs of degree 4 are stepwise. (2) To analyze precisely and possibly classify those HAT graphs of degree 4 with stepwise associated digraphs, where each level is the union of the set of tails of two alternating cycles (and at the same time the union of the set of heads of two alternating cycles). (3) Analyse exactly and possibly classify those HAT graphs of degree 4 with stepwise adjoint digraphs for which the subgroup of automorphisms preserving all levels is commutative.