{HEAD ~ The cutters} include at least two concentric arrays of {TAIL ~ primary preform polycrystalline diamond cutters} which are radially spaced so as to define an annular groove in the cutting profile, between the two arrays 
{ HEAD ~ The cutters } include at least two concentric arrays of { TAIL ~ primary preform polycrystalline diamond cutters } which are radially spaced so as to define an annular groove in the cutting profile , between the two arrays
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