/sci/ - Science & Math

>>11624276
I'm home and looking at the chapter.

Lemma 13.10 (vii) says if [math] F [/math] is [math] \Sigma_n[/math] , then to prove [math] F[/math] is [math] \Delta [/math] , we only need to show it for the domain. Although the prove of that statement itself is awfully short.
(This kind of thing was what I meant with using the graph-like aspect of the function set.)

And I suppose the [math] \alpha[/math] in [math] \alpha\mapsto L_\alpha[/math] is an ordinal, and the first line of proof 13.12 tells us that this domain, [math] {\mathrm Ord} [/math], is even [math] \Sigma_0 [/math]