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

verbatimtex
%&latex
\documentclass{article}
\begin{document}
etex
input graph
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defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
draw begingraph(250,150);
  pickup pencircle scaled 1pt;
  path p;
  for x=-20 step 0.2 until -0.2:
    augment.p (x, sind(x*180/3.14159)/x);
  endfor;
  augment.p (0, 1);
  for x=0.2 step 0.2 until 20:
    augment.p (x, sind(x*180/3.14159)/x);
  endfor;
  glabel.lrt(btex $\displaystyle\frac{\sin(x)}{x}$ etex,(-20,1));
  gdraw p;
endgraph
endfig;
end;