-- Mathlib/RingTheory/MvPowerSeries/Order.lean
theorem le_weightedOrder_mul :
    f.weightedOrder w + g.weightedOrder w ≤ weightedOrder w (f * g)

Proof state:
case h.mk
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Tactic:
by_cases hi : weight w i < f.weightedOrder w

Result:
case pos
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ↑((weight w) i) < weightedOrder w f
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ¬↑((weight w) i) < weightedOrder w f
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Proof state:
case h
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
⊢ ∀ x ∈ Finset.antidiagonal d, (coeff R x.1) f * (coeff R x.2) g = 0

Tactic:
rintro ⟨i, j⟩ hij

Result:
case h.mk
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Proof state:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
hij : i + j = d
⊢ ↑((weight w) d) = ↑((weight w) i) + ↑((weight w) j)

Tactic:
rw [← hij, map_add, Nat.cast_add]

Result:
no goals

Proof state:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ¬↑((weight w) i) < weightedOrder w f
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Tactic:
by_cases hj : weight w j < g.weightedOrder w

Result:
case pos
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ¬↑((weight w) i) < weightedOrder w f
hj : ↑((weight w) j) < weightedOrder w g
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ¬↑((weight w) i) < weightedOrder w f
hj : ¬↑((weight w) j) < weightedOrder w g
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Proof state:
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
⊢ weightedOrder w f + weightedOrder w g ≤ weightedOrder w (f * g)

Tactic:
apply le_weightedOrder

Result:
case h
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
⊢ ∀ (d : σ →₀ ℕ), ↑((weight w) d) < weightedOrder w f + weightedOrder w g → (coeff R d) (f * g) = 0

Proof state:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ¬↑((weight w) i) < weightedOrder w f
hj : ¬↑((weight w) j) < weightedOrder w g
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Tactic:
rw [not_lt] at hi hj

Result:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Proof state:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
hij : i + j = d
⊢ False

Tactic:
apply ne_of_lt (lt_of_lt_of_le hd <| add_le_add hi hj)

Result:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
hij : i + j = d
⊢ ↑((weight w) d) = ↑((weight w) i) + ↑((weight w) j)

Proof state:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
hij : i + j = d
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Tactic:
exfalso

Result:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
hij : i + j = d
⊢ False

Proof state:
case h
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
⊢ ∀ (d : σ →₀ ℕ), ↑((weight w) d) < weightedOrder w f + weightedOrder w g → (coeff R d) (f * g) = 0

Tactic:
intro d hd

Result:
case h
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
⊢ (coeff R d) (f * g) = 0

Proof state:
case h
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
⊢ (coeff R d) (f * g) = 0

Tactic:
rw [coeff_mul, Finset.sum_eq_zero]

Result:
case h
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
⊢ ∀ x ∈ Finset.antidiagonal d, (coeff R x.1) f * (coeff R x.2) g = 0

Proof state:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Tactic:
simp only [Finset.mem_antidiagonal] at hij

Result:
case neg
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hi : weightedOrder w f ≤ ↑((weight w) i)
hj : weightedOrder w g ≤ ↑((weight w) j)
hij : i + j = d
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Proof state:
case pos
σ : Type u_1
R : Type u_2
inst✝ : Semiring R
w : σ → ℕ
f g : MvPowerSeries σ R
d : σ →₀ ℕ
hd : ↑((weight w) d) < weightedOrder w f + weightedOrder w g
i j : σ →₀ ℕ
hij : (i, j) ∈ Finset.antidiagonal d
hi : ↑((weight w) i) < weightedOrder w f
⊢ (coeff R (i, j).1) f * (coeff R (i, j).2) g = 0

Tactic:
rw [coeff_eq_zero_of_lt_weightedOrder w hi, MulZeroClass.zero_mul]

Result:
no goals