@article{gurevich1983the,
author = {Gurevich, Yuri and Magidor, Menachem and Shelah, Saharon},
title = {The Monadic Theory of w2},
year = {1983},
month = {July},
abstract = {In a series of papers, Büchi proved the decidability of the monadic (second-order) theory of ω0, of all countable ordinals, of ω1, and finally of all ordinals < ω2. Here, assuming the consistency of a weakly compact cardinal, we prove that, in different set-theoretic worlds, the monadic theory of ω2 may be arbitrarily difficult (or easy).},
url = {http://approjects.co.za/?big=en-us/research/publication/monadic-theory-w2/},
pages = {387-398},
journal = {Journal of Symbolic Logic},
volume = {48},
}