code: def get_next_title_mark(lines):
      available_marks = ["=", "-", "~", "^"]
      for mark in available_marks:
          if has_token(mark * 3, lines):
              continue
          else:
              return mark
      return None
  
imports: import sys
  import os
  import re
label_desc: Use image node_id 2 for calling a global function with example usage: get_next_title_mark(lines) and returns: None, mark