def maxes(counter):
   """
   returns the max and a list of equivalent argmaxes
   """
   max, argmaxes = None, []
   for key in counter.keys():
       c = counter[key]
       if max == None or c > max:
           max = c
   for key in counter.keys():
       c = counter[key]
       if c == max:
           argmaxes.append(key)
   return max, argmaxes