% --- 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;