For example, referring to FIG 3, d1, separation between rows 320 and 321; d2, separation between rows 321 and 322; and d3, {HEAD ~ separation} between {TAIL ~ rows} 322 and 323; need not be equal, although in some embodiments of the invention, d1, d2 and d3 may be substantially equal 
between
For example , referring to FIG 3 , d1 , separation between rows 320 and 321 ; d2 , separation between rows 321 and 322 ; and d3 , { HEAD ~ separation } between { TAIL ~ rows } 322 and 323 ; need not be equal , although in some embodiments of the invention , d1 , d2 and d3 may be substantially equal
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