-- Mathlib/LinearAlgebra/TensorProduct/Graded/Internal.lean
theorem tmul_coe_mul_coe_tmul {j₁ i₂ : ι} (a₁ : A) (b₁ : ℬ j₁) (a₂ : 𝒜 i₂) (b₂ : B) :
    (a₁ ᵍ⊗ₜ[R] (b₁ : B) * (a₂ : A) ᵍ⊗ₜ[R] b₂ : 𝒜 ᵍ⊗[R] ℬ) =
      (-1 : ℤˣ)^(j₁ * i₂) • ((a₁ * a₂ : A) ᵍ⊗ₜ (b₁ * b₂ : B))

Proof state:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (-1) ^ (j₁ * i₂) •
      (of R 𝒜 ℬ)
        ((TensorProduct.congr (decomposeAlgEquiv 𝒜).toLinearEquiv (decomposeAlgEquiv ℬ).toLinearEquiv).symm
          (((decompose 𝒜) a₁ * (DirectSum.of (fun x => ↥(𝒜 x)) i₂) a₂) ⊗ₜ[R]
            ((DirectSum.of (fun x => ↥(ℬ x)) j₁) b₁ * (decompose ℬ) b₂))) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))

Tactic:
rw [congr_symm_tmul]

Result:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (-1) ^ (j₁ * i₂) •
      (of R 𝒜 ℬ)
        ((decomposeAlgEquiv 𝒜).toLinearEquiv.symm ((decompose 𝒜) a₁ * (DirectSum.of (fun x => ↥(𝒜 x)) i₂) a₂) ⊗ₜ[R]
          (decomposeAlgEquiv ℬ).toLinearEquiv.symm ((DirectSum.of (fun x => ↥(ℬ x)) j₁) b₁ * (decompose ℬ) b₂)) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))

Proof state:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ a₁ ᵍ⊗ₜ[R] ↑b₁ * ↑a₂ ᵍ⊗ₜ[R] b₂ = (-1) ^ (j₁ * i₂) • (a₁ * ↑a₂) ᵍ⊗ₜ[R] (↑b₁ * b₂)

Tactic:
dsimp only [mul_def, mulHom_apply, of_symm_of]

Result:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (auxEquiv R 𝒜 ℬ).symm
      (((gradedMul R (fun x => ↥(𝒜 x)) fun x => ↥(ℬ x)) ((auxEquiv R 𝒜 ℬ) (a₁ ᵍ⊗ₜ[R] ↑b₁)))
        ((auxEquiv R 𝒜 ℬ) (↑a₂ ᵍ⊗ₜ[R] b₂))) =
    (-1) ^ (j₁ * i₂) • (a₁ * ↑a₂) ᵍ⊗ₜ[R] (↑b₁ * b₂)

Proof state:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (-1) ^ (j₁ * i₂) •
      (of R 𝒜 ℬ)
        ((decompose 𝒜).symm ((decompose 𝒜) a₁ * (DirectSum.of (fun x => ↥(𝒜 x)) i₂) a₂) ⊗ₜ[R]
          (decompose ℬ).symm ((DirectSum.of (fun x => ↥(ℬ x)) j₁) b₁ * (decompose ℬ) b₂)) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))

Tactic:
simp_rw [decompose_symm_mul, decompose_symm_of, Equiv.symm_apply_apply]

Result:
no goals

Proof state:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (of R 𝒜 ℬ)
      ((TensorProduct.congr (decomposeAlgEquiv 𝒜).toLinearEquiv (decomposeAlgEquiv ℬ).toLinearEquiv).symm
        (((gradedMul R (fun x => ↥(𝒜 x)) fun x => ↥(ℬ x))
            ((decompose 𝒜) a₁ ⊗ₜ[R] (DirectSum.of (fun i => ↥(ℬ i)) j₁) b₁))
          ((DirectSum.of (fun i => ↥(𝒜 i)) i₂) a₂ ⊗ₜ[R] (decompose ℬ) b₂))) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))

Tactic:
simp_rw [← lof_eq_of R]

Result:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (of R 𝒜 ℬ)
      ((TensorProduct.congr (decomposeAlgEquiv 𝒜).toLinearEquiv (decomposeAlgEquiv ℬ).toLinearEquiv).symm
        (((gradedMul R (fun x => ↥(𝒜 x)) fun x => ↥(ℬ x)) ((decompose 𝒜) a₁ ⊗ₜ[R] (lof R ι (fun i => ↥(ℬ i)) j₁) b₁))
          ((lof R ι (fun i => ↥(𝒜 i)) i₂) a₂ ⊗ₜ[R] (decompose ℬ) b₂))) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))

Proof state:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (of R 𝒜 ℬ)
      ((TensorProduct.congr (decomposeAlgEquiv 𝒜).toLinearEquiv (decomposeAlgEquiv ℬ).toLinearEquiv).symm
        (((gradedMul R (fun x => ↥(𝒜 x)) fun x => ↥(ℬ x)) ((decompose 𝒜) a₁ ⊗ₜ[R] (lof R ι (fun i => ↥(ℬ i)) j₁) b₁))
          ((lof R ι (fun i => ↥(𝒜 i)) i₂) a₂ ⊗ₜ[R] (decompose ℬ) b₂))) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))

Tactic:
rw [tmul_of_gradedMul_of_tmul]

Result:
R : Type u_1
ι : Type u_2
A : Type u_3
B : Type u_4
inst✝⁹ : CommSemiring ι
inst✝⁸ : DecidableEq ι
inst✝⁷ : CommRing R
inst✝⁶ : Ring A
inst✝⁵ : Ring B
inst✝⁴ : Algebra R A
inst✝³ : Algebra R B
𝒜 : ι → Submodule R A
ℬ : ι → Submodule R B
inst✝² : GradedAlgebra 𝒜
inst✝¹ : GradedAlgebra ℬ
inst✝ : Module ι (Additive ℤˣ)
j₁ i₂ : ι
a₁ : A
b₁ : ↥(ℬ j₁)
a₂ : ↥(𝒜 i₂)
b₂ : B
⊢ (of R 𝒜 ℬ)
      ((TensorProduct.congr (decomposeAlgEquiv 𝒜).toLinearEquiv (decomposeAlgEquiv ℬ).toLinearEquiv).symm
        ((-1) ^ (j₁ * i₂) •
          ((decompose 𝒜) a₁ * (lof R ι (fun x => ↥(𝒜 x)) i₂) a₂) ⊗ₜ[R]
            ((lof R ι (fun x => ↥(ℬ x)) j₁) b₁ * (decompose ℬ) b₂))) =
    (-1) ^ (j₁ * i₂) • (of R 𝒜 ℬ) ((a₁ * ↑a₂) ⊗ₜ[R] (↑b₁ * b₂))