-- Mathlib/Algebra/MonoidAlgebra/Degree.lean
lemma supDegree_mul
    (hD : D.Injective) (hadd : ∀ a1 a2, D (a1 + a2) = D a1 + D a2)
    (hpq : leadingCoeff D p * leadingCoeff D q ≠ 0)
    (hp : p ≠ 0) (hq : q ≠ 0) :
    (p * q).supDegree D = p.supDegree D + q.supDegree D

Proof state:
case inr.hmem
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ leadingCoeff D p * leadingCoeff D q ≠ 0

Tactic:
exact hpq

Result:
no goals

Proof state:
case inr.hb
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ supDegree D p + supDegree D q ∈ { toFun := D, map_add' := hadd }.srange

Tactic:
exact add_mem (supDegree_mem_range D hp) (supDegree_mem_range D hq)

Result:
no goals

Proof state:
case inr.hmem
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ Function.invFun D (supDegree D p + supDegree D q) ∈ (p * q).support

Tactic:
simp_rw [Finsupp.mem_support_iff, apply_supDegree_add_supDegree hD hadd]

Result:
case inr.hmem
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ leadingCoeff D p * leadingCoeff D q ≠ 0

Proof state:
case inr.hmax
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
this✝ : CovariantClass B B (fun x1 x2 => x1 + x2) fun x1 x2 => x1 ≤ x2
this : CovariantClass B B (Function.swap fun x1 x2 => x1 + x2) fun x1 x2 => x1 ≤ x2
⊢ ∀ a ∈ (p * q).support, D a ≤ supDegree D p + supDegree D q

Tactic:
exact fun a ha => (Finset.le_sup ha).trans (supDegree_mul_le hadd)

Result:
no goals

Proof state:
case inl
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Subsingleton R
⊢ supDegree D (p * q) = supDegree D p + supDegree D q

Tactic:
exact (hp (Subsingleton.elim _ _)).elim

Result:
no goals

Proof state:
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
⊢ supDegree D (p * q) = supDegree D p + supDegree D q

Tactic:
cases subsingleton_or_nontrivial R

Result:
case inl
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Subsingleton R
⊢ supDegree D (p * q) = supDegree D p + supDegree D q

case inr
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ supDegree D (p * q) = supDegree D p + supDegree D q

Proof state:
case inr.hb
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ supDegree D p + supDegree D q ∈ Set.range D

Tactic:
rw [← AddSubsemigroup.coe_set_mk (Set.range D), ← AddHom.srange_mk _ hadd, SetLike.mem_coe]

Result:
case inr.hb
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ supDegree D p + supDegree D q ∈ { toFun := D, map_add' := hadd }.srange

Proof state:
case inr
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ supDegree D (p * q) = supDegree D p + supDegree D q

Tactic:
apply supDegree_eq_of_max

Result:
case inr.hb
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ supDegree D p + supDegree D q ∈ Set.range D

case inr.hmem
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ Function.invFun D (supDegree D p + supDegree D q) ∈ (p * q).support

case inr.hmax
R : Type u_1
A : Type u_3
B : Type u_5
inst✝⁶ : Semiring R
inst✝⁵ : LinearOrder B
inst✝⁴ : OrderBot B
p q : R[A]
D : A → B
inst✝³ : AddZeroClass A
inst✝² : Add B
inst✝¹ : AddLeftStrictMono B
inst✝ : AddRightStrictMono B
hD : Function.Injective D
hadd : ∀ (a1 a2 : A), D (a1 + a2) = D a1 + D a2
hpq : leadingCoeff D p * leadingCoeff D q ≠ 0
hp : p ≠ 0
hq : q ≠ 0
h✝ : Nontrivial R
⊢ ∀ a ∈ (p * q).support, D a ≤ supDegree D p + supDegree D q