A note on cover free families

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Let N((r,w;d),t) denote the minimum number of points in a (r,w;d)-cover-free family having t blocks. Hajiabolhassan and Moazami (2012)[6] showed that the Hadamard conjecture is equivalent to confirm N((1,1;d)4d-1)=4d-1. Hence, it is a challenging and interesting problem to determine the exact value of N((r,w;d),t). In this paper, we determine the exact value of N((r,w;d),t) for every r, w, where r+w<t+1 and some d.