fact: Definition step1 m n w (p : {poly R}) := \poly_(i < 2 ^ (m + n).+1) let j := (i %% 2 ^ n.+1)%N in if (j < 2 ^ n)%N then p`_i + p`_(i + 2 ^ n) * w ^+ j else p`_(i - 2 ^ n) - p`_i * w ^+ (j - 2 ^ n).
imports: mathcomp(all_ssreflect all_algebra ssrnum) digitn