old_contents: import collections
  
  
  def case_insensitive_counter(elements):
      counter = collections.Counter(elements)
  
      elements_lower = {}
      for element in counter:
          element_lower = element.lower()
          elements_lower.setdefault(element_lower, []).append(element)
  
      for _, cases in elements_lower.items():
          if len(cases) > 1:
              most_used_case = max(cases, key=lambda case: counter[case])
              total_occurrences = sum((counter[case] for case in cases))
              counter[most_used_case] = total_occurrences
              for case in cases:
                  if case != most_used_case:
                      del counter[case]
  
      return counter
  
new_contents: import collections
  
  
  def case_insensitive_counter(elements):
      counter = collections.Counter(elements)
  
      elements_lower = {}
      for element in counter:
          element_lower = element.lower()
          elements_lower.setdefault(element_lower, []).append(element)
  
      for _, cases in elements_lower.items():
          if len(cases) > 1:
              most_used_case = max(cases, key=counter.get)
              total_occurrences = sum(map(counter.get, cases))
              counter[most_used_case] = total_occurrences
              for case in cases:
                  if case != most_used_case:
                      del counter[case]
  
      return counter
  
subject: Reduce code verboseness