Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2024/ib/paper-1/19h/a/solution

Starting from , the probability of reaching before returning to is . Conditional on reaching , each visit to is followed by a hit on before the next return to with probability , by symmetry and the Strong Markov property. For , the number of visits after entry is therefore geometric on with mean . Hence the two-state excursion visit law gives
In the degenerate case , the chain never reaches before its return to , so almost surely and .

New to topics? Read the docs here!