code: def chebyshev4(c, x, domain):
      """Evaluate 4th order Chebyshev polynomial."""
      start_x, end_x = domain
      t = (x - 0.5 * (end_x + start_x)) / (0.5 * (end_x - start_x))
      return (
          c[0]
          + c[1] * t
          + c[2] * (2 * t**2 - 1)
          + c[3] * (4 * t**3 - 3 * t)
          - 0.5 * c[0]
      )
  
imports: import unittest
  from datetime import datetime, timedelta
  import dask.array
  import numpy
  import pytest
  import xarray
  from satpy.readers.seviri_base import MEIRINK_COEFS, MEIRINK_EPOCH, NoValidOrbitParams, OrbitPolynomial, OrbitPolynomialFinder, SEVIRICalibrationHandler, chebyshev, dec10216, get_cds_time, get_padding_area, get_satpos, pad_data_horizontally, pad_data_vertically, round_nom_time
  from satpy.utils import get_legacy_chunk_size
label_desc: Use image node_id 1 for calling a global function with example usage: chebyshev4(c, x, domain) and returns: unknown