A lazy quick sort

LazyQsort.cs

public static IEnumerable<T> LazyQsort<T>(IEnumerable<T> seq, Func<T, T, bool> comp)
{
	if (seq.Any() == false) 
	{
		return Enumerable.Empty<T>();
	}

	var pivot = seq.First();
	var xs = seq.Skip(1);
	return LazyQsort(xs.Where(x => comp (x, pivot)), comp)
		   .Union(new[] { pivot })
		   .Union(LazyQsort(xs.Where(x => !comp (x, pivot)), comp));
}

By using Enumerable.Empty<T>() you avoid a new initialisation everytime new T[0] gets called.