title: Diverging implicit expansion error using SortedSet
body: <p>I'm trying to use a code similar to</p>
  
  <pre><code>abstract class A[T] extends Ordered[A[T]] {
    val att:Int
  
    def compare(that:A[T]) = 
      if (this.att &gt;= that.att)
         1
      else
        -1
  }
  
  class B extends A[Int] {
    val att = 1
  }
  </code></pre>
  
  <p>When I try this in Scala 2.11 REPL</p>
  
  <pre><code>scala&gt; import scala.collection.immutable.SortedSet
  scala&gt; SortedSet[B]()
  </code></pre>
  
  <p>I get the following error</p>
  
  <pre><code>&lt;console&gt;:11: error: diverging implicit expansion for type Ordering[B]
  starting with method ordered in trait LowPriorityOrderingImplicits
            SortedSet[B]()
  </code></pre>
  
  <p>How can I solve this?</p>