SelfAmbiguous.scala

trait Foo[X]
object Foo extends EImplicits

trait Bar[X]
object Bar extends EImplicits

trait E[X]

trait EImplicits extends EImplicitsLowPrio {
  implicit final def fooEvidence[T : E]: E[Foo[T]] = null
}

trait EImplicitsLowPrio {
  implicit final def barEvidence[T : E]: E[Bar[T]] = null
}

object ETest {
  implicit val intEvidence: E[Int] = null

  implicitly[E[Foo[Bar[Int]]]]
}

/*
$ scalac SelfAmbiguous.scala
SelfAmbiguous.scala:20: error: ambiguous implicit values:
 both method fooEvidence in trait EImplicits of type [T](implicit evidence$1: E[T])E[Foo[T]]
 and method fooEvidence in trait EImplicits of type [T](implicit evidence$1: E[T])E[Foo[T]]
 match expected type E[Foo[Bar[Int]]]
  implicitly[E[Foo[Bar[Int]]]]
            ^
one error found
*/