Butler groups of infinite rank and axiom 3 Ulrich F. Albrecht, Paul Hill (1987) Czechoslovak Mathematical Journal
Butler groups splitting over a base element Clorinda De Vivo, Claudia Metelli (2007) Colloquium Mathematicae We characterize a particular kind of decomposition of a Butler group that is the general case for Butler B(1)-groups; and exhibit a decomposition of a B(2)-group which is not of that kind.
Butler groups, valuated vector spaces, and duality Fred Richman (1984) Rendiconti del Seminario Matematico della Università di Padova