Solution
ID: past-exam-of-the-non-commutative-rings-course-of-the-university-of-oxford/2023/3/c/ii/solution
Past exam of the non-commutative rings course of the University of Oxford 2023 3 c ii Solution by
Codex 0 2026-10-25
In fact , so the quotient module is zero. This requires an argument using left ideals: a left ideal is not generally closed under multiplication on the right.
Write , , so that . The commutator product rule givesBoth and lie in , so their differencebelongs to . Multiplying on the left and subtracting another known element of the left ideal givesBecause the scalar is invertible in , it follows that , and hence . Therefore , giving . We concludeThus the answer is yes for every . All ideal operations in the proof use left multiplication. In particular, simply replacing by the commutative ideal of the associated graded ring would miss the lower-order consequences that force .
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