Solution

ID: past-exam-of-the-probability-statistics-and-options-ii-course-of-the-university-of-oxford/2010/d/d4/1/a/solution

The th derivative of the integrand is , whose absolute value is at most one. The integration interval has finite measure. Repeated application of the differentiation theorem therefore gives
Dominated convergence also gives continuity of every derivative, proving infinite differentiability.

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