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Mathlib.RingTheory.Radical

Radical of an element of a unique factorization normalization monoid #

This file defines a radical of an element a of a unique factorization normalization monoid, which is defined as a product of normalized prime factors of a without duplication. This is different from the radical of an ideal.

Main declarations #

For unique factorization domains #

For Euclidean domains #

For natural numbers #

TODO #

The finite set of prime factors of an element in a unique factorization monoid.

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      If x is a unit, then the finset of prime factors of x is empty. The converse is true with a nonzero assumption, see normalizedFactors_eq_zero_iff.

      The finset of prime factors of x is empty if and only if x is a unit. The converse is true without the nonzero assumption, see primeFactors_of_isUnit.

      Relatively prime elements have disjoint prime factors (as finsets).

      Radical of an element a in a unique factorization monoid is the product of the prime factors of a.

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          @[deprecated UniqueFactorizationMonoid.radical_zero (since := "2025-05-31")]

          Alias of UniqueFactorizationMonoid.radical_zero.

          @[deprecated UniqueFactorizationMonoid.radical_one (since := "2025-05-31")]

          Alias of UniqueFactorizationMonoid.radical_one.

          If a is a radical element, then it divides its radical.

          An irreducible a divides the radical of b if and only if it divides b itself. Note this generalises to radical elements a, see UniqueFactorizationMonoid.dvd_radical_iff.

          If a divides b, then the radical of a divides the radical of b. The theorem requires that b ≠ 0, since radical 0 = 1 but a ∣ 0 holds for every a.

          If a is a radical element, then a divides the radical of b if and only if it divides b. Note the forward implication holds without the b ≠ 0 assumption via radical_dvd_self.

          Radical is multiplicative for relatively prime elements.

          theorem UniqueFactorizationMonoid.radical_prod {M : Type u_1} [CancelCommMonoidWithZero M] [NormalizationMonoid M] [UniqueFactorizationMonoid M] {ι : Type u_2} {f : ιM} (s : Finset ι) (h : (↑s).Pairwise (Function.onFun IsRelPrime f)) :
          radical (∏ is, f i) = is, radical (f i)
          theorem UniqueFactorizationMonoid.radical_prod_dvd {M : Type u_1} [CancelCommMonoidWithZero M] [NormalizationMonoid M] [UniqueFactorizationMonoid M] {ι : Type u_2} {s : Finset ι} {f : ιM} :
          radical (∏ is, f i) is, radical (f i)

          Theorems for UFDs

          @[deprecated "UniqueFactorizationMonoid.disjoint_normalizedFactors, IsCoprime.isRelPrime" (since := "2025-05-31")]

          Coprime elements have disjoint prime factors (as multisets).

          @[deprecated "UniqueFactorizationMonoid.disjoint_primeFactors, IsCoprime.isRelPrime" (since := "2025-05-31")]

          Coprime elements have disjoint prime factors (as finsets).

          @[deprecated "UniqueFactorizationMonoid.primeFactors_mul_eq_disjUnion, IsCoprime.isRelPrime" (since := "2025-05-31")]
          @[deprecated "UniqueFactorizationMonoid.radical_mul, IsCoprime.isRelPrime" (since := "2025-05-31")]

          Radical is multiplicative for coprime elements.

          Division of an element by its radical in an Euclidean domain.

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