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1)Let D be a 2−(v,k,λ) design with b blocks and r blocks through every point. Let B be any block. How to show that the number of blocks that meet B is at least $k(r−1)^2/[(k−1)(λ−1)+(r−1)]$

2) How to show that if v<=k+t then a t design is trivial?

3)Is a complement of a t design is also a design?

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What have you tried? –  azimut Mar 7 '13 at 18:42
tomorrow is exam –  efj Mar 7 '13 at 19:27

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