def delete(key, options = {})
      @stack.inject(nil) do |value, s|
        v = s.delete(key, options)
        value || v
      end
    end
def delete(key, options = {})
      @stack.inject(nil) do |value, s|
        v = s.delete(key, options)
        value || v
      end
    end
(see Proxy#delete)