{TAIL ~ The forcer} is {HEAD ~ a periodic device} for incrementally moving in a normally open loop configuration over a toothed base element or platen, and can be a linear or other stepper motor system 
{ TAIL ~ The forcer } is { HEAD ~ a periodic device } for incrementally moving in a normally open loop configuration over a toothed base element or platen , and can be a linear or other stepper motor system
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