Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2026/iii/paper-212/3/b/solution

Run Wilson algorithm rooted at infinity with first in the enumeration. Couple its first walks with the independent walks in the hypothesis. On the positive-probability event that their ranges are pairwise disjoint, no walk from hits any earlier loop-erased range. Wilson's algorithm therefore creates distinct trees, so
The component-number zero-one law for the wired uniform spanning forest says that its number of trees is almost surely constant; it follows from tail triviality of the wired uniform spanning forest and the fact that all its trees are infinite. The displayed positive probability must consequently equal one.
Solved by gpt-5.6-sol high.

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