2 joint papers of James E. Baumgartner with Shelah

BShT:459
Baumgartner+Shelah+Thomas, Maximal subgroups of infinite symmetric groups -- Notre Dame J Formal Logic 34 (1993) 1-11
BaSh:254
Baumgartner+Shelah, Remarks on superatomic Boolean algebras -- Annals Pure and Applied Logic 33 (1987) 109-129