Module: Mathlib.RingTheory.MvPolynomial.EulerIdentity

Goal state before:
pp: case refine_1
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
⊢ ∀ x ∈ (fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n}, IsWeightedHomogeneous w ((pderiv i) x) n'

pp: case refine_2
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
⊢ IsWeightedHomogeneous w ((pderiv i) 0) n'

pp: case refine_3
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
p q : MvPolynomial σ R
x✝¹ : p ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
x✝ : q ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
hp : IsWeightedHomogeneous w ((pderiv i) p) n'
hq : IsWeightedHomogeneous w ((pderiv i) q) n'
⊢ IsWeightedHomogeneous w ((pderiv i) (p + q)) n'

pp: case refine_4
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h✝ : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
r : R
p : MvPolynomial σ R
x✝ : p ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h : IsWeightedHomogeneous w ((pderiv i) p) n'
⊢ IsWeightedHomogeneous w ((pderiv i) (r • p)) n'

Tactic:
· rintro _ ⟨m, hm, rfl⟩
    simp_rw [single_eq_monomial, pderiv_monomial, one_mul]
    by_cases hi : m i = 0
    · rw [hi, Nat.cast_zero, monomial_zero]; apply isWeightedHomogeneous_zero
    convert! isWeightedHomogeneous_monomial ..
    rw [← add_right_cancel_iff (a := w i), h', ← hm, weight_sub_single_add hi]

Goal state after:
case refine_2
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
⊢ IsWeightedHomogeneous w ((pderiv i) 0) n'

case refine_3
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
p q : MvPolynomial σ R
x✝¹ : p ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
x✝ : q ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
hp : IsWeightedHomogeneous w ((pderiv i) p) n'
hq : IsWeightedHomogeneous w ((pderiv i) q) n'
⊢ IsWeightedHomogeneous w ((pderiv i) (p + q)) n'

case refine_4
R : Type u_1
σ : Type u_2
M : Type u_3
inst✝¹ : CommSemiring R
φ : MvPolynomial σ R
inst✝ : AddCancelCommMonoid M
w : σ → M
n n' : M
i : σ
h✝ : φ ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h' : n' + w i = n
r : R
p : MvPolynomial σ R
x✝ : p ∈ Submodule.span R ((fun m ↦ AddMonoidAlgebra.single m 1) '' {d | (weight w) d = n})
h : IsWeightedHomogeneous w ((pderiv i) p) n'
⊢ IsWeightedHomogeneous w ((pderiv i) (r • p)) n'