code: func FprintCDF(w io.Writer, dists ...stats.Dist) error {
  	xscale, xs := commonScale(dists...)
  	for _, d := range dists {
  		if err := fprintFn(w, d.CDF, xscale, xs); err != nil {
  			return err
  		}
  	}
  	return fprintScale(w, xscale)
  }
docs: // FprintCDF is equivalent to FprintPDF, but prints the CDF of each
  // distribution.