Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2022/iii/paper-160/1/b/solution

The assumed one-dimensional-image property gives
for some . The coefficient of in is one, so
The tabloid bilinear form is invariant, and the involution on the group algebra fixes the Column antisymmetrizer of a Young tableau because inversion preserves sign. Therefore
which proves the formula.

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