var query = from n in Runner.Defects
				    orderby n.Assembly.Name.FullName
				    group n by n.Rule.Name into a
				    select new {
					    RuleName = a.Key,
// here I'd like at have Problem and Solution (both properties of n.Rule)
					    Value = from o in a
						      group o by o.Target.ToString () into r
						      select new { Target = r.Key, Value = r }
				    };