Kurepa tree from an inaccessible binary tree
ID: kurepa-tree-from-an-inaccessible-binary-tree
Let be strongly inaccessible cardinal in the ground model and perform the finite Lévy collapse to omega-one. The ground full binary set-theoretic tree of height has all levels of size less than , so these levels become countable. Its at least ground branches remain distinct. The chain in a partial order condition preserves , which is the extension . The unchanged ground set-theoretic tree therefore witnesses the Kurepa hypothesis.
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