theorem WellFounded.ofTransGen {α : Type u_1} {r : α → α → Prop} (trans_wf : WellFounded (Relation.TransGen r)) : WellFounded r

@[simp]

theorem WellFounded.iff_transGen {α : Type u_1} {r : α → α → Prop} : WellFounded (Relation.TransGen r) ↔ WellFounded r

Relations

References

• Term Rewriting and All That

theorem Relation.ReflGen.to_eqvGen {α : Type u_1} {r : α → α → Prop} {a b : α} (h : ReflGen r a b) : EqvGen r a b

theorem Relation.TransGen.to_eqvGen {α : Type u_1} {r : α → α → Prop} {a b : α} (h : TransGen r a b) : EqvGen r a b

theorem Relation.ReflTransGen.to_eqvGen {α : Type u_1} {r : α → α → Prop} {a b : α} (h : ReflTransGen r a b) : EqvGen r a b

theorem CompRel.to_eqvGen {α : Type u_1} {r : α → α → Prop} {a b : α} (h : CompRel r a b) : Relation.EqvGen r a b

def Relation.UpTo {α : Type u_1} (r s : α → α → Prop) : α → α → Prop

The relation r 'up to' the relation s.

Equations

• Relation.UpTo r s = Relation.Comp s (Relation.Comp r s)

@[reducible, inline]

abbrev Relation.Diamond {α : Type u_1} (r : α → α → Prop) : Prop

A relation has the diamond property when all reductions with a common origin are joinable

Equations

• Relation.Diamond r = ∀ {a b c : α}, r a b → r a c → Relation.Join r b c

@[reducible, inline]

abbrev Relation.Confluent {α : Type u_1} (r : α → α → Prop) : Prop

A relation is confluent when its reflexive transitive closure has the diamond property.

Equations

• Relation.Confluent r = Relation.Diamond (Relation.ReflTransGen r)

@[reducible, inline]

abbrev Relation.SemiConfluent {α : Type u_1} (r : α → α → Prop) : Prop

A relation is semi-confluent when single and multiple steps with common origin are multi-joinable.

Equations

• Relation.SemiConfluent r = ∀ {x y₁ y₂ : α}, Relation.ReflTransGen r x y₂ → r x y₁ → Relation.Join (Relation.ReflTransGen r) y₁ y₂

@[reducible, inline]

abbrev Relation.ChurchRosser {α : Type u_1} (r : α → α → Prop) : Prop

A relation has the Church Rosser property when equivalence implies multi-joinability.

Equations

• Relation.ChurchRosser r = ∀ {x y : α}, Relation.EqvGen r x y → Relation.Join (Relation.ReflTransGen r) x y

theorem Relation.Diamond.extend {α : Type u_1} {r : α → α → Prop} {a b c : α} (h : Diamond r) : ReflTransGen r a b → r a c → Join (ReflTransGen r) b c

Extending a multistep reduction by a single step preserves multi-joinability.

theorem Relation.Diamond.toConfluent {α : Type u_1} {r : α → α → Prop} (h : Diamond r) : Confluent r

The diamond property implies confluence.

theorem Relation.Confluent.toChurchRosser {α : Type u_1} {r : α → α → Prop} (h : Confluent r) : ChurchRosser r

theorem Relation.SemiConfluent.toConfluent {α : Type u_1} {r : α → α → Prop} (h : SemiConfluent r) : Confluent r

theorem Relation.SemiConfluent_iff_ChurchRosser {α : Type u_1} {r : α → α → Prop} : SemiConfluent r ↔ ChurchRosser r

theorem Relation.Confluent_iff_ChurchRosser {α : Type u_1} {r : α → α → Prop} : Confluent r ↔ ChurchRosser r

theorem Relation.Confluent_iff_SemiConfluent {α : Type u_1} {r : α → α → Prop} : Confluent r ↔ SemiConfluent r

@[reducible, inline]

abbrev Relation.Reducible {α : Type u_1} (r : α → α → Prop) (x : α) : Prop

An element is reducible with respect to a relation if there is a value it is related to.

Equations

• Relation.Reducible r x = ∃ (y : α), r x y

@[reducible, inline]

abbrev Relation.Normal {α : Type u_1} (r : α → α → Prop) (x : α) : Prop

An element is normal if it is not reducible.

Equations

• Relation.Normal r x = ¬Relation.Reducible r x

theorem Relation.Normal.reflTransGen_eq {α : Type u_1} {r : α → α → Prop} {x y : α} (h : Normal r x) (xy : ReflTransGen r x y) : x = y

A multi-step from a normal form must be reflexive.

theorem Relation.ChurchRosser.normal_eqvGen_reflTransGen {α : Type u_1} {r : α → α → Prop} {x y : α} (cr : ChurchRosser r) (norm : Normal r x) (xy : EqvGen r y x) : ReflTransGen r y x

For a Church-Rosser relation, elements in an equivalence class must be multi-step related.

theorem Relation.ChurchRosser.normal_eq {α : Type u_1} {r : α → α → Prop} {x y : α} (cr : ChurchRosser r) (nx : Normal r x) (ny : Normal r y) (xy : EqvGen r x y) : x = y

For a Church-Rosser relation there is one normal form in each equivalence class.

def Relation.trans_of_subrelation {α : Type u_1} (s s' r : α → α → Prop) (hr : Transitive r) (h : Subrelation s r) (h' : Subrelation s' r) : Trans s s' r

A pair of subrelations lifts to transitivity on the relation.

Equations

• Relation.trans_of_subrelation s s' r hr h h' = { trans := ⋯ }

def Relation.trans_of_subrelation_left {α : Type u_1} (s r : α → α → Prop) (hr : Transitive r) (h : Subrelation s r) : Trans s r r

A subrelation lifts to transitivity on the left of the relation.

Equations

• Relation.trans_of_subrelation_left s r hr h = { trans := ⋯ }

def Relation.trans_of_subrelation_right {α : Type u_1} (s r : α → α → Prop) (hr : Transitive r) (h : Subrelation s r) : Trans r s r

A subrelation lifts to transitivity on the right of the relation.

Equations

• Relation.trans_of_subrelation_right s r hr h = { trans := ⋯ }

theorem Relation.Confluent.equivalence_join_reflTransGen {α : Type u_1} {r : α → α → Prop} (h : Confluent r) : Equivalence (Join (ReflTransGen r))

Confluence implies that multi-step joinability is an equivalence.

@[reducible, inline]

abbrev Relation.Terminating {α : Type u_1} (r : α → α → Prop) : Prop

A relation is terminating when the inverse of its transitive closure is well-founded. Note that this is also called Noetherian or strongly normalizing in the literature.

Equations

• Relation.Terminating r = WellFounded fun (a b : α) => r b a

theorem Relation.Terminating.toTransGen {α : Type u_1} {r : α → α → Prop} (ht : Terminating r) : Terminating (TransGen r)

theorem Relation.Terminating.ofTransGen {α : Type u_1} {r : α → α → Prop} : Terminating (TransGen r) → Terminating r

theorem Relation.Terminating.iff_transGen {α : Type u_1} {r : α → α → Prop} : Terminating (TransGen r) ↔ Terminating r

@[reducible, inline]

abbrev Relation.LocallyConfluent {α : Type u_1} (r : α → α → Prop) : Prop

A relation is locally confluent when all reductions with a common origin are multi-joinable

Equations

• Relation.LocallyConfluent r = ∀ {a b c : α}, r a b → r a c → Relation.Join (Relation.ReflTransGen r) b c

theorem Relation.Confluent.toLocallyConfluent {α : Type u_1} {r : α → α → Prop} (h : Confluent r) : LocallyConfluent r

theorem Relation.LocallyConfluent.Terminating_toConfluent {α : Type u_1} {r : α → α → Prop} (hlc : LocallyConfluent r) (ht : Terminating r) : Confluent r

Newman's lemma: a terminating, locally confluent relation is confluent.

@[reducible, inline]

abbrev Relation.StronglyConfluent {α : Type u_1} (r : α → α → Prop) : Prop

A relation is strongly confluent when single steps are reflexive- and multi-joinable.

Equations

• Relation.StronglyConfluent r = ∀ {x y₁ y₂ : α}, r x y₁ → r x y₂ → ∃ (z : α), Relation.ReflGen r y₁ z ∧ Relation.ReflTransGen r y₂ z

def Relation.Commute {α : Type u_1} (r₁ r₂ : α → α → Prop) : Prop

Generalization of Confluent to two relations.

Equations

• Relation.Commute r₁ r₂ = ∀ {x y₁ y₂ : α}, Relation.ReflTransGen r₁ x y₁ → Relation.ReflTransGen r₂ x y₂ → ∃ (z : α), Relation.ReflTransGen r₂ y₁ z ∧ Relation.ReflTransGen r₁ y₂ z

theorem Relation.Commute.symmetric {α : Type u_1} : Symmetric Commute

theorem Relation.Commute.toConfluent {α : Type u_1} {r : α → α → Prop} : Commute r r = Confluent r

def Relation.StronglyCommute {α : Type u_1} (r₁ r₂ : α → α → Prop) : Prop

Generalization of StronglyConfluent to two relations.

Equations

• Relation.StronglyCommute r₁ r₂ = ∀ {x y₁ y₂ : α}, r₁ x y₁ → r₂ x y₂ → ∃ (z : α), Relation.ReflGen r₂ y₁ z ∧ Relation.ReflTransGen r₁ y₂ z

theorem Relation.StronglyCommute.toStronglyConfluent {α : Type u_1} {r : α → α → Prop} : StronglyCommute r r = StronglyConfluent r

def Relation.DiamondCommute {α : Type u_1} (r₁ r₂ : α → α → Prop) : Prop

Generalization of Diamond to two relations.

Equations

• Relation.DiamondCommute r₁ r₂ = ∀ {x y₁ y₂ : α}, r₁ x y₁ → r₂ x y₂ → ∃ (z : α), r₂ y₁ z ∧ r₁ y₂ z

theorem Relation.DiamondCommute.toDiamond {α : Type u_1} {r : α → α → Prop} : DiamondCommute r r = Diamond r

theorem Relation.StronglyCommute.extend {α✝ : Type u_2} {r₁ r₂ : α✝ → α✝ → Prop} {x y z : α✝} (h : StronglyCommute r₁ r₂) (xy : ReflTransGen r₁ x y) (xz : r₂ x z) : ∃ (w : α✝), ReflGen r₂ y w ∧ ReflTransGen r₁ z w

theorem Relation.StronglyCommute.toCommute {α✝ : Type u_2} {r₁ r₂ : α✝ → α✝ → Prop} (h : StronglyCommute r₁ r₂) : Commute r₁ r₂

theorem Relation.StronglyConfluent.toConfluent {α : Type u_1} {r : α → α → Prop} (h : StronglyConfluent r) : Confluent r

theorem Relation.join_inl {α : Type u_1} {r₁ r₂ : α → α → Prop} {a b : α} (r₁_ab : r₁ a b) : max r₁ r₂ a b

theorem Relation.join_inr {α : Type u_1} {r₁ r₂ : α → α → Prop} {a b : α} (r₂_ab : r₂ a b) : max r₁ r₂ a b

theorem Relation.join_inl_reflTransGen {α : Type u_1} {r₁ r₂ : α → α → Prop} {a b : α} (r₁_ab : ReflTransGen r₁ a b) : ReflTransGen (r₁ ⊔ r₂) a b

theorem Relation.join_inr_reflTransGen {α : Type u_1} {r₁ r₂ : α → α → Prop} {a b : α} (r₂_ab : ReflTransGen r₂ a b) : ReflTransGen (r₁ ⊔ r₂) a b

theorem Relation.Commute.join_left {α : Type u_1} {r₁ r₂ r₃ : α → α → Prop} (c₁ : Commute r₁ r₃) (c₂ : Commute r₂ r₃) : Commute (r₁ ⊔ r₂) r₃

theorem Relation.Commute.join_confluent {α : Type u_1} {r₁ r₂ : α → α → Prop} (c₁ : Confluent r₁) (c₂ : Confluent r₂) (comm : Commute r₁ r₂) : Confluent (r₁ ⊔ r₂)

theorem Relation.reflTransGen_mono_closed {α : Type u_1} {r₁ r₂ : α → α → Prop} (h₁ : Subrelation r₁ r₂) (h₂ : Subrelation r₂ (ReflTransGen r₁)) : ReflTransGen r₁ = ReflTransGen r₂

If a relation is squeezed by a relation and its multi-step closure, they are multi-step equal

theorem Relation.ReflGen.compRel_symm {α : Type u_1} {r : α → α → Prop} {a b : α} : ReflGen (CompRel r) a b → ReflGen (CompRel r) b a

@[simp]

theorem Relation.reflTransGen_compRel {α : Type u_1} {r : α → α → Prop} : ReflTransGen (CompRel r) = EqvGen r