This is more of a graph problem. You are given set A={1,2,..,n}. You have to create sets B(i) for all i=1,2,..,n, such that i $\notin$ B(i). The constraint on set are the following: 1) If $j \in B(i)$ then $ i \notin B(j)$. 2) For all i $\in$ B(j), {B(j) $\setminus$ i }$\not \subset$ B(i). 3) For all i $\notin$ B(k), B(i) $\not \subset$ {k $\cup$ B(k)} Can such subsets be created. I can prove it for n=4,5,6 but I am not able to generalise it. I have an opinion that such subsets cannot be created.