input: def count_unique_letters_in_both_cases(s: str) -> int:
      """
      You have a string s. A character is considered unique if it can be found in both its uppercase and lowercase forms in s.
  
      Determine the count of unique characters in s.
  
      Examples:
      >>> s = "aaAbcBC"
      3
      >>> s = "abc"
      0
      >>> s = "abBCab"
      1
  
      Constraints:
      1 <= s.length <= 50
      s includes only lowercase and uppercase English letters.
      """
output:     
      lower_set = set()
      upper_set = set()
  
      for char in s:
          if char.islower():
              lower_set.add(char)
          elif char.isupper():
              upper_set.add(char)
  
      unique_count = 0
      for char in lower_set:
          if char.upper() in upper_set:
              unique_count += 1
  
      return unique_count
  