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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mtf_bitransformer_tiny():
 """Small encoder-decoder model for testing."""

  hparams = mtf_bitransformer_base()
  hparams.batch_size = 2
  hparams.mesh_shape = ""
  hparams.d_model = 128
  hparams.encoder_layers = ["self_att", "drd"] * 2
  hparams.decoder_layers = ["self_att", "enc_att", "drd"] * 2
  hparams.num_heads = 4
  hparams.d_ff = 512
  return hparams