Constructibility
Keith J. Devlin
If U is transitive, then the rud closure of U is transitive. Proof. Let W be the rud
closure of U. We prove by induction on a rud definition off that for any rud function
f: V"- V and any x1, ..., x, e W. (*) TC(x1) g W.A ... A TC(x,) c W-> TC(f(x1,..., xn)) G
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