Here we go: it is referred to as dual copula theory and an encouraging note on the plato page on non-existent objects: ” it is beyond doubt that Neo-Meinongian theories can be and indeed are fruitful in many ways. In particular, they provide the basis for a consistent realist ontology of fictitious objects. (For a variety of further applications see in particular the writings of Jacquette, Parsons, and Zalta.)” https://en.wikipedia.org/wiki/Round_square_copula

and an encouraging note on the plato page on non-existent objects:

” it is beyond doubt that Neo-Meinongian theories can be and indeed are fruitful in many ways. In particular, they provide the basis for a consistent realist ontology of fictitious objects. (For a variety of further applications see in particular the writings of Jacquette, Parsons, and Zalta.)”