input: Write a function to create a 3x3 matrix using list comprehension.
  assert create_matrix() == [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
  assert create_matrix()[0] == [1, 2, 3]
  assert create_matrix()[2] == [7, 8, 9]
output: def create_matrix():
      return [[i + j*3 + 1 for i in range(3)] for j in range(3)]