Solution

ID: past-exam-of-the-analysis-course-of-the-university-of-oxford/2009/a/3/iii/solution

The weighted right shift is injective, so zero is not an eigenvalue. If with , the first coordinate forces and subsequent coordinates force every . Thus its point spectrum is empty.
For ,
since the largest column sum is attained at . Therefore the spectral radius formula gives . The limit follows, for example, from for large . Zero is in the spectrum because the output first coordinate is always zero, so is not onto. Hence
This is a nonzero quasinilpotent element, specifically the factorial weighted right shift.

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