def add(token, timestamp = nil)
      @net.call_callbacks(:place, :add, Event.new(@name, [token], @net)) unless @net.nil?
      if timestamp.nil?
        @marking.add token
      else
        @marking.add token, timestamp
      end
    end
def add(token, timestamp = nil)
      @net.call_callbacks(:place, :add, Event.new(@name, [token], @net)) unless @net.nil?
      if timestamp.nil?
        @marking.add token
      else
        @marking.add token, timestamp
      end
    end
Adds token with specified timestamp to the place.
 Any callbacks defined for places will be fired.