Find duplicate items in multiple lists

gistfile1.cs

List<List<string>> lists = new List<List<string>>() {
    new List<string> {"Hello", "World", "7"},
    new List<string> {"Hello", "7", "Person"},
    new List<string> {"7", "7", "Hello"}
};
 
List<string> common = lists.Cast<IEnumerable<string>>(
                           .Aggregate( ( a, b ) => a.Intersect( b ) )
                           .ToList();