2-Colourings in S(t, t + 1, v)

Let S(t, k, v) be any nontrivial Steiner system. In this paper we prove the nonexistence of 2-colourings in Steiner systems S(t, t + 1, v) when t + 1 is an odd number. Further, we prove that if t + 1 is an even number and C is a blocking set of the system S(t, t + 1, v) then ¦C¦=v/2.