beginfig(1)
  u := 1cm;

  pair t;
  t = dir (60);

  pair a[];
  pair b[];
  a0 = (0, 0);
  b0 = (u, 0);
  
  for i=1 upto 6:
    pair c[];
    pair d[];
    c0 = a[i-1];
    d0 = b[i-1];
    for j=1 upto 5:
      c[j] = c[j-1] + d[j-1];
      draw c[j-1]--c[j];
      d[j] = (xpart t * xpart d[j-1] - ypart t * ypart d[j-1],
        xpart t * ypart d[j-1] + ypart t * xpart d[j-1]);
    endfor;
    a[i] = a[i-1] + b[i-1];
    b[i] = (xpart t * xpart b[i-1] + ypart t * ypart b[i-1],
      xpart t * ypart b[i-1] - ypart t * xpart b[i-1]);
  endfor;

  dotlabel.lrt("0", 1/2[a0, a3]+(-5, 5));
endfig;