  Current deterministic algorithms for the construction of polar codes can only
be argued to be practical for channels with small input alphabet sizes. In this
paper, we show that any construction algorithm for channels with moderate input
alphabet size which follows the paradigm of "degrading after each polarization
step" will inherently be impractical with respect to a certain "hard"
underlying channel. This result also sheds light on why the construction of
LDPC codes using density evolution is impractical for channels with moderate
sized input alphabets.
