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