  The number of low-weight codewords is critical to the performance of
error-correcting codes. In 1970, Kasami and Tokura characterized the codewords
of Reed-Muller (RM) codes whose weights are less than $2w_{\min}$, where
$w_{\min}$ represents the minimum weight. In this paper, we extend their
results to decreasing polar codes. We present the closed-form expressions for
the number of codewords in decreasing polar codes with weights less than
$2w_{\min}$. Moreover, the proposed enumeration algorithm runs in polynomial
time with respect to the code length.
