# mathlib3documentation

ring_theory.ore_localization.ore_set

# (Right) Ore sets #

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This defines right Ore sets on arbitrary monoids.

## References #

@[class]
structure ore_localization.ore_set {R : Type u_1} [monoid R] (S : submonoid R) :
Type u_1

A submonoid S of a monoid R is (right) Ore if common factors on the left can be turned into common factors on the right, and if each pair of r : R and s : S admits an Ore numerator v : R and an Ore denominator u : S such that r * u = s * v.

Instances of this typeclass
Instances of other typeclasses for ore_localization.ore_set
• ore_localization.ore_set.has_sizeof_inst
theorem ore_localization.ore_left_cancel {R : Type u_1} [monoid R] {S : submonoid R} (r₁ r₂ : R) (s : S) (h : s * r₁ = s * r₂) :
(s' : S), r₁ * s' = r₂ * s'

Common factors on the left can be turned into common factors on the right, a weak form of cancellability.

def ore_localization.ore_num {R : Type u_1} [monoid R] {S : submonoid R} (r : R) (s : S) :
R

The Ore numerator of a fraction.

Equations
def ore_localization.ore_denom {R : Type u_1} [monoid R] {S : submonoid R} (r : R) (s : S) :

The Ore denominator of a fraction.

Equations
theorem ore_localization.ore_eq {R : Type u_1} [monoid R] {S : submonoid R} (r : R) (s : S) :
r * =

The Ore condition of a fraction, expressed in terms of ore_num and ore_denom.

def ore_localization.ore_condition {R : Type u_1} [monoid R] {S : submonoid R} (r : R) (s : S) :
Σ' (r' : R) (s' : S), r * s' = s * r'

The Ore condition bundled in a sigma type. This is useful in situations where we want to obtain both witnesses and the condition for a given fraction.

Equations
@[protected, instance]

The trivial submonoid is an Ore set.

Equations
@[protected, instance]

Every submonoid of a commutative monoid is an Ore set.

Equations
def ore_localization.ore_set_of_cancel_monoid_with_zero {R : Type u_1} {S : submonoid R} (ore_num : R S R) (ore_denom : R S S) (ore_eq : (r : R) (s : S), r * (ore_denom r s) = s * ore_num r s) :

Cancellability in monoids with zeros can act as a replacement for the ore_left_cancel condition of an ore set.

Equations
def ore_localization.ore_set_of_no_zero_divisors {R : Type u_1} [ring R] {S : submonoid R} (ore_num : R S R) (ore_denom : R S S) (ore_eq : (r : R) (s : S), r * (ore_denom r s) = s * ore_num r s) :

In rings without zero divisors, the first (cancellability) condition is always fulfilled, it suffices to give a proof for the Ore condition itself.

Equations