A new short proof of a theorem of Ahlswede and Khachatrian

Ahlswede and Khachatrian [R. Ahlswede, L.H. Khachatrian, The complete nontrivial-intersection theorem for systems of finite sets, J. Combin. Theory Ser. A 76 (1996) 121-138] proved the following theorem, which answered a question of Frankl and Furedi [P. Frankl, Z. Furedi, Nontrivial intersecting families, J. Combin. Theory Ser. A 41 (1986) 150-153]. Let 2==(t+1)(k-t+1). Suppose that F is a family of k-subsets of an n-set, every two of which have at least t common elements. If |@?"F"@?"FF|