code: def plot_vs(fignum, Xs, c, ls):
      
      fig = plt.figure(num=fignum)
      for xv in Xs:
          bounds = plt.axis()
          plt.axvline(
              x=xv, ymin=bounds[2], ymax=bounds[3], linewidth=1, color=c, linestyle=ls)
docs: plots  vertical lines at Xs values
  
      Parameters
      _________
      fignum : matplotlib figure number
      Xs : list of X values for lines
      c : color for lines
      ls : linestyle for lines