Solution

ID: past-exam-of-the-lie-algebras-course-of-part-c-of-the-mathematics-course-of-the-university-of-oxford/2023/1/d/solution

Let be a three-dimensional vector space with basis . Define a bilinear map by
with all other products of basis vectors zero. Equivalently,
Every product belongs to , and every product with an element of is zero. Hence both and vanish for every . This proves associativity, so is an associative algebra. The product is an alternating multilinear map, and each nested product in the Jacobi identity is zero, so the same product is a Lie bracket. It is nonzero because .
There is no multiplicative identity element: any candidate would satisfy , whereas an identity element would require . Thus
This is an associative Lie product; its underlying Lie algebra is the Heisenberg Lie algebra.

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