docs: def polynomial_multiply_mod( m1, m2, polymod, p ):
    """Polynomial multiplication modulo a polynomial over ints mod p.
  
    Polynomials are represented as lists of coefficients
    of increasing powers of x."""
  
    # This is just a seat-of-the-pants implementation.
  
    # This module has been tested only by extensive use
    # in calculating modular square roots.
  
    # Initialize the product to zero:
  
    prod = ( len( m1 ) + len( m2 ) - 1 ) * [0]
  
    # Add together all the cross-terms:
  
    for i in range( len( m1 ) ):
      for j in range( len( m2 ) ):
        prod[i+j] = ( prod[i+j] + m1[i] * m2[j] ) % p
  
    return polynomial_reduce_mod( prod, polymod, p )