nth_rw 1 [p.leadingTerms.as_sum]
case left
R : Type u_1
ι : Type u_2
inst✝ : CommSemiring R
p : MvPolynomial ι R
hp : p.totalDegree ≠ 0
this : DecidableEq ι := Classical.decEq ι
⊢ p = p.leadingTerms + ∑ v ∈ p.support \ p.leadingTerms.support, (monomial v) (coeff v p)
case left
R : Type u_1
ι : Type u_2
inst✝ : CommSemiring R
p : MvPolynomial ι R
hp : p.totalDegree ≠ 0
this : DecidableEq ι := Classical.decEq ι
⊢ p =
    ∑ v ∈ p.leadingTerms.support, (monomial v) (coeff v p.leadingTerms) +
      ∑ v ∈ p.support \ p.leadingTerms.support, (monomial v) (coeff v p)