Question

Set Theory - Show that there is an ordinal y with y=Ay

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Some definitions: Ordinal is a transitive set (X is a transitive set iff for all y in X, y is a subset of X) that is strictly well ordered by epsilon (every non empty subset has a minimum).

Fix an ordinal q. A0 = q. Ax+1= Ax U {Ax}.

Show that there is an ordinal y with y=Ay.