docs: def polynomial_reduce_mod( poly, polymod, p ):
    """Reduce poly by polymod, integer arithmetic modulo p.
  
    Polynomials are represented as lists of coefficients
    of increasing powers of x."""
  
    # This module has been tested only by extensive use
    # in calculating modular square roots.
  
    # Just to make this easy, require a monic polynomial:
    assert polymod[-1] == 1
  
    assert len( polymod ) > 1
  
    while len( poly ) >= len( polymod ):
      if poly[-1] != 0:
        for i in range( 2, len( polymod ) + 1 ):
          poly[-i] = ( poly[-i] - poly[-1] * polymod[-i] ) % p
      poly = poly[0:-1]
  
    return poly