Two-part and k-Sperner families: New proofs using permutations

This is a paper about the beauty of the permutation method. New and shorter proofs are given for the theorem [ P. L. Erd. os and G. O. H. Katona, J. Combin. Theory. Ser. A, 43 ( 1986), pp. 58 – 69; S. Shahriari, Discrete Math., 162 ( 1996), pp. 229 – 238] determining all extremal two-part Sperner families and for the uniqueness of k-Sperner families of maximum size [ P. Erd. os, Bull. Amer. Math. Soc., 51 ( 1945), pp. 898 – 902].