-- Mathlib/RingTheory/PiTensorProduct.lean
lemma algebraMap_apply (r : R') (i : ι) [DecidableEq ι] :
    algebraMap R' (⨂[R] i, A i) r = tprod R (Pi.mulSingle i (algebraMap R' (A i) r))

Proof state:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
⊢ Pi.mulSingle i (r • 1) = update (fun i => 1) i (r • 1)

Tactic:
rfl

Result:
no goals

Proof state:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
⊢ r • (tprod R) 1 = (tprod R) (Pi.mulSingle i ((algebraMap R' (A i)) r))

Tactic:
have : Pi.mulSingle i (algebraMap R' (A i) r) = update (fun i ↦ 1) i (r • 1) := by
  rw [Algebra.algebraMap_eq_smul_one]; rfl

Result:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
this : Pi.mulSingle i ((algebraMap R' (A i)) r) = update (fun i => 1) i (r • 1)
⊢ r • (tprod R) 1 = (tprod R) (Pi.mulSingle i ((algebraMap R' (A i)) r))

Proof state:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
⊢ (algebraMap R' (⨂[R] (i : ι), A i)) r = (tprod R) (Pi.mulSingle i ((algebraMap R' (A i)) r))

Tactic:
change r • tprod R 1 = _

Result:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
⊢ r • (tprod R) 1 = (tprod R) (Pi.mulSingle i ((algebraMap R' (A i)) r))

Proof state:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
this : Pi.mulSingle i ((algebraMap R' (A i)) r) = update (fun i => 1) i (r • 1)
⊢ r • (tprod R) 1 = (tprod R) (Pi.mulSingle i ((algebraMap R' (A i)) r))

Tactic:
rw [this, ← smul_one_smul R r (1 : A i), MultilinearMap.map_update_smul, update_eq_self,
  smul_one_smul, Pi.one_def]

Result:
no goals

Proof state:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
⊢ Pi.mulSingle i ((algebraMap R' (A i)) r) = update (fun i => 1) i (r • 1)

Tactic:
rw [Algebra.algebraMap_eq_smul_one]

Result:
ι : Type u_1
R' : Type u_2
R : Type u_3
A : ι → Type u_4
inst✝⁷ : CommSemiring R'
inst✝⁶ : CommSemiring R
inst✝⁵ : (i : ι) → Semiring (A i)
inst✝⁴ : Algebra R' R
inst✝³ : (i : ι) → Algebra R (A i)
inst✝² : (i : ι) → Algebra R' (A i)
inst✝¹ : ∀ (i : ι), IsScalarTower R' R (A i)
r : R'
i : ι
inst✝ : DecidableEq ι
⊢ Pi.mulSingle i (r • 1) = update (fun i => 1) i (r • 1)