Firstly, {HEAD ~ an S bent line} is arranged as {TAIL ~ a fundamental element} by connecting two circular arcs having respective curvatures inverted relative to each other, namely, upward convex and downward convex circular arcs 
is arranged as
Firstly , { HEAD ~ an S bent line } is arranged as { TAIL ~ a fundamental element } by connecting two circular arcs having respective curvatures inverted relative to each other , namely , upward convex and downward convex circular arcs
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH