code: def match_head(subject, pattern):
      
      if isinstance(pattern, Pattern):
          pattern = pattern.expression
      pattern_head = get_head(pattern)
      if pattern_head is None:
          return True
      if issubclass(pattern_head, OneIdentityOperation):
          return True
      subject_head = get_head(subject)
      assert subject_head is not None
      return issubclass(subject_head, pattern_head)
docs: Checks if the head of subject matches the pattern's head.