code: def build_single_mosaic(
      mosaic_images_list: List[np.ndarray],
  ) -> np.ndarray:
      """
      Frame a list of 4 images into a 2x2 mosaic image.
  
      Parameters
      ----------
      mosaic_images_list: List[np.array]
          A list of four images.
  
      Returns
      -------
      mosaic: np.ndarray
           The single 2x2 mosaic built from a list of images.
      """
      first_row = np.concatenate(
          (mosaic_images_list[0], mosaic_images_list[1]), axis=1
      )
      second_row = np.concatenate(
          (mosaic_images_list[2], mosaic_images_list[3]), axis=1
      )
      mosaic = np.concatenate((first_row, second_row), axis=2)
      return mosaic
  
imports: import math
  import random
  from typing import List, Tuple, Optional, Union, Any
  import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: build_single_mosaic(mosaic_images_list) and returns: mosaic