DerivedScala.scala:4: error: class C needs to be abstract, since there is a deferred declaration of method foo in class B of type => Int which is not implemented in a subclass
class C extends B
      ^
DerivedScala.scala:7: error: class DerivedScala needs to be abstract, since there is a deferred declaration of method foo in class Abstract of type ()Boolean which is not implemented in a subclass
class DerivedScala extends Abstract
      ^
two errors found