code: def format_crossvalidation(is_inverted, n, k):
      cv_type = "Inverted" if is_inverted else "Classical"
      return "{}:{};{}".format(cv_type, n, k)
  
imports: import collections
  import csv
  import json
  import os
  import random
  import shutil
  import sys
  from pandas import read_csv, DataFrame
  from copy import deepcopy
  import numpy
  from catboost.utils import read_cd
label_desc: Use image node_id 15 for calling a global function with example usage: format_crossvalidation(is_inverted, n, k) and returns: str