A dropping proof of an entropy inequality

Abstract A simple proof of the entropy inequality due to Chung, Graham, Frankl and Shearer [F.R.K. Chung, R.L. Graham, P. Frankl, J.B. Shearer, Some intersection theorems for ordered sets and graphs, J. Combin. Theory Ser. A 43 (1) (1986) 23–37] is given by proposing a “dropping method” based on the strong subadditivity of the joint entropy.