t2066.scala:6: error: overriding method f in trait A1 of type [T[_]]=> Unit;
 method f has incompatible type
  override def f[T[+_]] = ()
               ^
t2066.scala:10: error: overriding method f in trait A1 of type [T[_]]=> Unit;
 method f has incompatible type
  override def f[T[-_]] = ()
               ^
t2066.scala:23: error: overriding method f in trait A2 of type [T[+_]]=> Unit;
 method f has incompatible type
  override def f[T[-_]] = ()
               ^
t2066.scala:45: error: overriding method f in trait A4 of type [T[X[+_]]]=> Unit;
 method f has incompatible type
  override def f[T[X[_]]] = ()
               ^
t2066.scala:53: error: overriding method f in trait A5 of type [T[X[-_]]]=> Unit;
 method f has incompatible type
  override def f[T[X[_]]] = ()
               ^
5 errors found