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The Lumenary

Practice · First-year graduate

Commutative algebra

Commutative algebra

Warm-upHuman

Which of these ideals are prime? (Choose all that apply.)

Choose all that apply

Commutative algebra

Warm-upHuman

What is the Krull dimension of Z[x]\mathbb{Z}[x]?

Commutative algebra

CoreHuman

How many elements does the localisation (Z/360)(3)(\mathbb{Z}/360)_{(3)} have? (Here (3)(3) is the prime ideal of Z/360\mathbb{Z}/360 generated by 33.)

Commutative algebra

CoreHuman

In the proof of Hilbert's basis theorem, Ld⊆RL_d \subseteq R is the ideal of leading coefficients of degree-dd elements of I⊆R[x]I \subseteq R[x]. Why is there an NN with LN=LN+1=LN+2=⋯L_N = L_{N+1} = L_{N+2} = \cdots?

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Commutative algebra

CoreHuman

Let R=Z(p)R = \mathbb{Z}_{(p)}, m=pZ(p)\mathfrak{m} = p\mathbb{Z}_{(p)} and M=QM = \mathbb{Q}. Then mM=M\mathfrak{m}M = M but M≠0M \neq 0. Which hypothesis of Nakayama's lemma fails?

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Commutative algebra

StretchHuman

Let I=(x2+y2−1,  x−1)⊆C[x,y]I = (x^2 + y^2 - 1,\; x - 1) \subseteq \mathbb{C}[x, y]: the unit circle and its tangent line at (1,0)(1, 0). Which of these polynomials lie in II itself? (Choose all that apply.)

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Commutative algebra

CoreFormal

Which Lean statement formalises “the polynomial ring in infinitely many variables over a field kk is not Noetherian”?

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Commutative algebra

StretchComputational

The ideals of Z/n\mathbb{Z}/n are dZ/nZd\mathbb{Z}/n\mathbb{Z} for the divisors dd of nn. Write prime_ideals(n) (for n≥2n \ge 2) returning the sorted list of divisors dd of nn for which the ideal generated by dd in Z/n\mathbb{Z}/n is prime, checking the definition directly: proper, and ab∈I⇒a∈Iab \in I \Rightarrow a \in I or b∈Ib \in I for all residues a,ba, b.

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