T. Parsons, Nonexistent Objects, 1980.

S. Yablo, Textbook Kripkeanism and the Open Texture of Concepts, Pacific Philosophical Quarterly, vol.81, issue.1, pp.98-122, 2000.
DOI : 10.1111/1468-0114.00097

E. Zalta, Intensional Logic and the Metaphysics of Intentionality The Modal Object Calculus and Its Interpretation, Advances in Intensional Logic, M. De Rijke, pp.249-279, 1988.