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

% --- end of displayed preamble in the book ---
defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
  numeric u;
  u=3cm;
  special("(this is a PostScript comment!)");
  z0=origin;
  z1-z0=(u,u);
  z2-z1=(-u,-.5u);
  draw z0..z1{dir-50}..z2;
  special("(this is another PostScript comment!)");
  special("(z2 will be located at ("
    & decimal x2 & "," & decimal y2 & "))");
endfig;
end;