The cusps shown in FIGS 3 and 4 are of course, cross sections of modules as exemplified in FIG 1, and can be extended indefinitely in {HEAD ~ a direction} perpendicular to {TAIL ~ the section plane} 
perpendicular to
The cusps shown in FIGS 3 and 4 are of course , cross sections of modules as exemplified in FIG 1 , and can be extended indefinitely in { HEAD ~ a direction } perpendicular to { TAIL ~ the section plane }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL