select within(GROUP,within(3.5,hbpositive) and hbnegative, 
within(3.5,hbnegative) and hbpositive)
wireframe 50
cpk 100
color cpk
select within(3.5,hbpositive) and hbnegative
connect 3.5 (within(3.5,hbnegative) and hbpositive) hbonds