Blueprint of Groebner Basis Theory in LEAN

1 Definitions

Definition 1 withBotDegree
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the degree of a multivariate polynomial with respect to a monomial ordering

Definition 2 toWithBotSyn
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Definition 3 «term_≺’[_]_»
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Given a monomial order with bot, notation for the corresponding strict order relation on WithBot (σ →₀ ℕ)

Definition 4 «term_≼’[_]_»
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Given a monomial order with bot, notation for the corresponding order relation on WithBot (σ →₀ ℕ)

Definition 5 IsRemainder
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Given a multivariate polynomial f and a set B of multivariate polynomials over R. A polynomial r is called a remainder of f on division by B with respect to a monomial order m, if there exists g : B →₀ R[X] and a polynomial r s.t.

  1. Finite linear combination: f = ∑ (g(b) * b) + r;

  2. Degree condition: For eacho b ∈ B, the degree (with bot) of g(b) * b ≤ the degree (with bot) of f w.r.t. m;

  3. Remainder irreducibility: No term of r is divisible by the leading monomial of any non-zero b ∈ B.

The definition of remainder makes sense when R is a communitive ring and any polynomial in B either has an invertible leading coefficient or is 0. See the implementation note for the formalization unaligned with the informal definition when not in this case.

Definition 6 IsGroebnerBasis
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A subset G of an ideal I is said to be a Gröbner basis if:

  1. G is contained in I (i.e., all polynomials in G belong to the ideal I).

  2. The ideal generated by the leading terms of all polynomials in I is equal to the ideal generated by the leading terms of the polynomials in G.

Definition 7 subset
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Definition 8 span_leadingTerm_image
Definition 9 isGroebnerBasis_iff
Definition 10 IsMinimal
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Definition 11 isMinimal_def
Definition 12 monic
Definition 13 pairwise
Definition 14 IsReduced
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