input: Write a function to add two matrices. If the matrices are not compatible for addition, return 'Matrices not compatible'. Otherwise, return the result of the addition. If one of the matrices is empty or if both matrices are empty, return 'Matrices not compatible'.
  
  def add_matrix(matrix1, matrix2):
      if not matrix1 or not matrix2:
          return 'Matrices not compatible'
      if len(matrix1) != len(matrix2) or len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      result = [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]
      
      return result
  
  assert add_matrix([[1, 2], [3, 4]], [[2, 3], [4, 5]]) == [[3, 5], [7, 9]]
  assert add_matrix([[1, 2, 3], [4, 5, 6]], [[7, 8, 9], [10, 11, 12]]) == [[8, 10, 12], [14, 16, 18]]
  assert add_matrix([[1, 2], [3, 4]], [[1], [2]]) == 'Matrices not compatible'
  assert add_matrix([], [[1, 2], [3, 4]]) == 'Matrices not compatible'
  assert add_matrix([[1, 2], [3, 4]], []) == 'Matrices not compatible'
output: def add_matrix(matrix1, matrix2):
      if not matrix1 or not matrix2:
          return 'Matrices not compatible'
      if len(matrix1) != len(matrix2) or len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      result = [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]
      
      return result