oop question

hi all
i have 2classes in my namespace like follow:

namespace myNameSpace
{
   public  class ClBase :ClChild
    {}
  abstract class ClChild
    {}
}
ClBase Inherits all elements from  ClChild.
it makes error (because ClChild is abstract or internal and ClBase is Public),i must declare my ClChild as public , i dont want use public for ClChild because out of this project another tier can see clchild and i dont want  it for my security ,now
How can i have ClChild class that clBase can inherities all elements on ClChild and  ClChild dont be a public???????
Please Help me.

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