% --- start of displayed preamble in the book ---

% --- end of displayed preamble in the book ---
defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
pickup pencircle scaled 3pt
   yscaled .2pt rotated 60;
n:=5;
for i := (n*20) step -(n) until (n):
 draw ((i,0)..(0,i)..(-i,0)
      ..(0,-(i-n))..(i-n,0)) scaled 0.7;
endfor
endfig;
end;