t2918.scala:2: error: illegal cyclic reference involving type A
  def g[X, A[X] <: A[X]](x: A[X]) = x
                                    ^
t2918.scala:2: error: cyclic aliasing or subtyping involving type A
  def g[X, A[X] <: A[X]](x: A[X]) = x
           ^
t2918.scala:2: error: A does not take type parameters
  def g[X, A[X] <: A[X]](x: A[X]) = x
                            ^
three errors found