engleski

On the 2-Y -homogeneous condition of the incidence graphs of 2-designs

We discuss the 2-Y -homogeneous condition of the incidence graphs of 2-designs. We prove that quasi-symmetric 2-designs that are quasi-symmetric 3-(v, k, λ) designs with intersection numbers 0 and y = λ + 1 are the only 2-designs which have 2- Y -homogeneous distance-biregular incidence graphs. Moreover, every 2-Y -homogeneous distance- biregular graph with eccentricity D = 3 is the incidence graph of such a design.

distance-biregular graph, incidence graph, 2-design

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