, 1996, Existence and correspondence-to-fact, in R. Poli & P. Simons (eds.), Formal ontology, Dordrecht, Springer, pp. 131-158.
, 1974a, The logical and the extra-logical, in R. S. Cohen & M. W. Wartofsky (eds.), Methodological and historical essays in the natural and social sciences, Dordrecht, Springer, pp. 235-252.