input: Write a Python function to perform matrix multiplication for 2x2 matrices.
  assert matrix_mult([[1, 2], [3, 4]], [[4, 3], [2, 1]]) == [[8, 5], [20, 13]]
  assert matrix_mult([[2, 0], [1, 2]], [[1, 2], [3, 4]]) == [[2, 4], [7, 10]]
  assert matrix_mult([[0, 1], [1, 0]], [[1, 0], [0, 1]]) == [[0, 1], [1, 0]]
output: def matrix_mult(A, B):
      return [
          [
              A[0][0] * B[0][0] + A[0][1] * B[1][0],
              A[0][0] * B[0][1] + A[0][1] * B[1][1]
          ],
          [
              A[1][0] * B[0][0] + A[1][1] * B[1][0],
              A[1][0] * B[0][1] + A[1][1] * B[1][1]
          ]
      ]