Theorem: Algebra.EssFiniteType.algHom_ext
File: Mathlib/RingTheory/EssentialFiniteness.lean

Proof steps:
state_before: R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f = g
state_after: R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f.toRingHom = g.toRingHom
tactic: suffices f.toRingHom = g.toRingHom by ext; exact RingHom.congr_fun this _
state_before: R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f.toRingHom = g.toRingHom
state_after: case h
R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f.comp (algebraMap (↥(subalgebra R S)) S) = g.comp (algebraMap (↥(subalgebra R S)) S)
tactic: apply IsLocalization.ringHom_ext (EssFiniteType.submonoid R S)
state_before: case h
R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f.comp (algebraMap (↥(subalgebra R S)) S) = g.comp (algebraMap (↥(subalgebra R S)) S)
state_after: case h
R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f.comp (IsScalarTower.toAlgHom R (↥(subalgebra R S)) S) = g.comp (IsScalarTower.toAlgHom R (↥(subalgebra R S)) S)
tactic: suffices f.comp (IsScalarTower.toAlgHom R _ S) = g.comp (IsScalarTower.toAlgHom R _ S) by
    ext; exact AlgHom.congr_fun this _
state_before: case h
R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ f.comp (IsScalarTower.toAlgHom R (↥(subalgebra R S)) S) = g.comp (IsScalarTower.toAlgHom R (↥(subalgebra R S)) S)
state_after: case h.h
R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ adjoin R {x | ↑x ∈ finset R S} = ⊤

case h.hs
R : Type u_1
S : Type u_2
T : Type u_3
inst✝⁷ : CommRing R
inst✝⁶ : CommRing S
inst✝⁵ : CommRing T
inst✝⁴ : Algebra R S
inst✝³ : Algebra R T
inst✝² : Algebra S T
inst✝¹ : IsScalarTower R S T
inst✝ : EssFiniteType R S
f g : S →ₐ[R] T
H : ∀ s ∈ finset R S, f s = g s
⊢ Set.EqOn ⇑(f.comp (IsScalarTower.toAlgHom R (↥(subalgebra R S)) S))
    ⇑(g.comp (IsScalarTower.toAlgHom R (↥(subalgebra R S)) S)) {x | ↑x ∈ finset R S}
tactic: apply AlgHom.ext_of_adjoin_eq_top (s := { x | x.1 ∈ finset R S })