Quasi-symmetric designs with y = λ

AbstractWe discuss 2-(υ, k, λ) designs with two intersecion numbers the larger of which is λ. We show that for each λ there are only finitely many feasible parameter sets. We find all parameter sets with λ less than 400 and smaller intersection at least 2. These satisfy further conditions. We determine all sets satisfying these conditions finding two sporadic sets and two infinite families. The first sets of parameters from one of the families is realized by a design of V. Tonchev