GenericsLoop.java

interface Z {}
interface N<T> {}

interface E<T> extends N<N<? super E<? super T>>> {}

// Changing E to the following, Oracle JDK 1.8.0_92 says
// `error: incompatible types: E<Z> cannot be converted to N<? super E<Z>>`
// interface E<T> extends N<N<? super E<T>>> {}

class GenericsLoop {
    N<? super E<Z>> doit(E<Z> v) {
        /*
           E → NNE

             EZ <: NEZ
                ↓
           NNEZ <: NEZ
                ↓
             EZ <: NEZ
        */

        return v;
    }
}

GenericsLoopFewerSuper.java

interface Z {}
interface N<T> {}

interface E<T> extends N<N<? super E<N<T>>>> {}

class Main {
    N<? super E<Z>> doit(E<Z> v) {
        /*
           E → NN?EN
               EZ <: N?EZ
                  ↓
           NN?ENZ <: N?EZ
                  ↓
               EZ <: N?ENZ
                  ↓
           NN?ENZ <: N?ENZ
                  ↓
              ENZ <: N?ENZ
                  ↓*
             ENNZ <: N?ENNZ
                  ↓*
            ENNNZ <: N?ENNNZ
                  ↓
                  .
                  .
                  .
        */

        return v;
    }
}

loop1.scala

trait Z
trait N[T]

// error: illegal cyclic reference involving trait E
trait E[T] extends N[N[_ >: E[N[T]]]]

class Main {
  def doit(v: E[Z]): N[_ >: E[Z]] = v
}

loop2.scala

trait Z
trait N[-T]

// error: class graph is not finitary because type parameter T is expansively recursive
trait E[-T] extends N[N[E[N[T]]]]

class Main {
  def doit(v: E[Z]): N[E[Z]] = v
}

loop3.scala

trait Z
trait N[-T]
trait E[-T] extends N[N[E[_ >: T]]]

class Main {
  def doit(v: E[Z]): N[E[Z]] = v
}