% --- start of displayed preamble in the book --- % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) pickup pencircle scaled 4pt yscaled .2pt rotated 60; n:=4; for i := (n*20) step -(n) until (n): c:=((n*20)-i)/(n*2); draw (i,0)..(0,i)..(-i,0) ..(0,-(i-n))..(i-n,0) withcolor ((100-i)/100,i/100,0); endfor endfig; end;