Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2022/iii/paper-204/1/d/solution

Because itself is a tree, every finite induced connected exhaustion has the unique spanning tree consisting of all its edges. Thus its free spanning forest is deterministically .
By the stated transience criterion, choose an edge whose two complementary subtrees are transient. Run Wilson algorithm rooted at infinity first from . With positive probability its loop-erased walk remains forever in the -side. Starting next from , there is likewise positive conditional probability that its walk remains forever in the -side. On this event the two rays never use , so is absent from the wired uniform spanning forest. The wired law is therefore not the deterministic free law.

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