{HEAD ~ The covers} enclose a cartridge extension mechanism capable of extending the pen cartridge from the housing upon application of a pressure to the respective covers, and retracting the pen cartridge into the housing upon removal of the pressure from {TAIL ~ the covers} 
{ HEAD ~ The covers } enclose a cartridge extension mechanism capable of extending the pen cartridge from the housing upon application of a pressure to the respective covers , and retracting the pen cartridge into the housing upon removal of the pressure from { TAIL ~ the covers }
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