Test.scala:4: error: type mismatch;
 found   : Array[Int]
 required: Array[? with Object]
Note: Int >: ? with Object, but class Array is invariant in type T.
You may wish to investigate a wildcard type such as `_ >: ? with Object`. (SLS 3.2.10)
  AO.f(a)
       ^
Test.scala:5: error: type mismatch;
 found   : Array[Int]
 required: Array[Int]
Note: Int >: Int, but class Array is invariant in type T.
You may wish to investigate a wildcard type such as `_ >: Int`. (SLS 3.2.10)
  AO.f[Int](a)
            ^
two errors found