code: def crop_bezier(seg, t0, t1):
      
      assert t0 < t1
      if t0 == 0:
          cropped_seg = seg.split(t1)[0]
      elif t1 == 1:
          cropped_seg = seg.split(t0)[1]
      else:
          pt1 = seg.point(t1)
  
          # trim off the 0 <= t < t0 part
          trimmed_seg = crop_bezier(seg, t0, 1)
  
          # find the adjusted t1 (i.e. the t1 such that
          # trimmed_seg.point(t1) ~= pt))and trim off the t1 < t <= 1 part
          t1_adj = trimmed_seg.radialrange(pt1)[0][1]
          cropped_seg = crop_bezier(trimmed_seg, 0, t1_adj)
      return cropped_seg
docs: returns a cropped copy of this segment which starts at self.point(t0)
      and ends at self.point(t1).