Hi,

I need to show that there is a set A of ordinals (von Neumann) with a largest elementasuch that UA (union of A) is strictly less thana. But ifais an element of A and UA is ina, then UA is an element of itself.

I'm probably missing something very simple here, but any help would be much appreciated.

Regards

Sam

For reference, the problem is in Discovering Modern Set Theory: The ... - Google Books

page 159.