Scala's existential type cannot emulate Java's Wildcard

console.txt

Undecidable.scala:6: error: illegal cyclic reference involving trait E
trait E[X] extends AnyRef with Qlr[N[_ >: Qr[_ >: E[_ >: E[_ >: X]]]]] with Qrl[N[_ >: Ql[_ >: E<_ >: E[_ >: X]]]]
                                                    ^
Undecidable.scala:6: error: E does not take type parameters
trait E[X] extends AnyRef with Qlr[N[_ >: Qr[_ >: E[_ >: E[_ >: X]]]]] with Qrl[N[_ >: Ql[_ >: E<_ >: E[_ >: X]]]]
                                                  ^
Undecidable.scala:8: error: illegal cyclic reference involving trait Qr
trait Qr[X] extends AnyRef with L[N[_ >: Qr[_ >: L[_ >: N[_ >: X]]]]] with E[Qrl[_ >: N[_ >: X]]]
                                    ^
Undecidable.scala:8: error: E does not take type parameters
trait Qr[X] extends AnyRef with L[N[_ >: Qr[_ >: L[_ >: N[_ >: X]]]]] with E[Qrl[_ >: N[_ >: X]]]

        ^
Undecidable.scala:6: error: E does not take type parameters
trait E[X] extends AnyRef with Qlr[N[_ >: Qr[_ >: E[_ >: E[_ >: X]]]]] with Qrl[N[_ >: Ql[_ >: E<_ >: E[_ >: X]]]]

                                   ^
Undecidable.scala:6: error: not found: type <
trait E[X] extends AnyRef with Qlr[N[_ >: Qr[_ >: E[_ >: E[_ >: X]]]]] with Qrl[N[_ >: Ql[_ >: E<_ >: E[_ >: X]]]]

                             ^
Undecidable.scala:7: error: illegal cyclic reference involving trait Ql
trait Ql[X] extends AnyRef with L[N[_ >: Ql[_ >: L[_ >: N[_ >: X]]]]] with E[Qlr[_ >: N[_ >: X]]]
                                    ^
Undecidable.scala:7: error: E does not take type parameters
trait Ql[X] extends AnyRef with L[N[_ >: Ql[_ >: L[_ >: N[_ >: X]]]]] with E[Qlr[_ >: N[_ >: X]]]

        ^
Undecidable.scala:10: error: type mismatch;
 found   : Qr[_$21] where type _$21 >: E[_ >: E[_ >: Z]]
 required: L[_ >: N[_ >: L[_ >: N[_ >: L[_ >: N[_ >: E[_ >: E[_ >: Z]]]]]]]]
Note: _$21 <: Any, but trait L is invariant in type X.
You may wish to define X as +X instead. (SLS 4.5)
  def doIt(v: Qr[_ >: E[_ >: E[_ >: Z]]]): L[_ >: N[_ >: L[_ >: N[_ >: L[_ >: N[_ >: E[_ >: E[_ >: Z]]]]]]]] = v

                                            ^
9 errors found

Undecidable.scala

trait Z
trait N[X]
trait L[X]
trait Qlr[X]
trait Qrl[X]
trait E[X] extends AnyRef with Qlr[N[_ >: Qr[_ >: E[_ >: E[_ >: X]]]]] with Qrl[N[_ >: Ql[_ >: E<_ >: E[_ >: X]]]]
trait Ql[X] extends AnyRef with L[N[_ >: Ql[_ >: L[_ >: N[_ >: X]]]]] with E[Qlr[_ >: N[_ >: X]]]
trait Qr[X] extends AnyRef with L[N[_ >: Qr[_ >: L[_ >: N[_ >: X]]]]] with E[Qrl[_ >: N[_ >: X]]]
object Undecidable {
  def doIt(v: Qr[_ >: E[_ >: E[_ >: Z]]]): L[_ >: N[_ >: L[_ >: N[_ >: L[_ >: N[_ >: E[_ >: E[_ >: Z]]]]]]]] = v
}
/*
  interface Z {} interface N<x> {} interface L<x> {}
  interface Qlr<x> {} interface Qrl<x> {}
  interface E<x> extends
  Qlr<N<?super Qr<?super E<?super E<?super x>>>>>,
  Qrl<N<?super Ql<?super E<?super E<?super x>>>>> {}
  interface Ql<x> extends
  L<N<?super Ql<?super L<?super N<?super x>>>>>,
  E<Qlr<?super N<?super x>>> {}
  interface Qr<x> extends
  L<N<?super Qr<?super L<?super N<?super x>>>>>,
  E<Qrl<?super N<?super x>>> {}
  class Main {
  L<?super N<?super L<?super N<?super L<?super N<?super
  E<?super E<?super Z>>>>>>>>
  doit(Qr<? super E<? super E<? super Z>>> v) {return v;}
  }
*/