C# 3.0: Need to return duplicates from a List<>

Question

I have a List<> of objects in C# and I need a way to return those objects that are considered duplicates within the list. I do not need the Distinct resultset, I need a

Answer 1

public static IQueryable Duplicates(this IEnumerable source) where TSource : IComparable {

if (source == null)   
     throw new ArgumentNullException("source");   
 return source.Where(x => source.Count(y=>y.Equals(x)) > 1).AsQueryable();   

}