3 ms·
Set family {{1,2,3,4}, {1}, {2}, {3}, {4}} has all 4 elements appearing in exactly 2 sets out of the 5, that is 40%. What am I missing?
by notgettingit 4y ago
Set family {{1,2,3,4}, {1}, {2}, {3}, {4}} has all 4 elements appearing in exactly 2 sets out of the 5, that is 40%. What am I missing?
- jdkee 4y agoYour example is not union-closed. "A collection, or family, of sets is considered “union-closed” if the union of any two sets in the family equals any existing set in the family." EDIT: In your hypothetical collection of sets, the union of "2" and "3" would produce the set "2,3" which is not an enumerated set in your list.
- scapp 4y agoCheck out the replies to this comment [1] with the same attempted counterexample. Your set isn't union closed because {1}U{2} = {1, 2} isn't in it (same for {1}U{3} etc.). [1] https://news.ycombinator.com/item?id=34236889#34240381 https://news.ycombinator.com/item?id=34236889#34240381