Undefinability of propositional quantifiers in the modal system S4

@article{Ghilardi1995UndefinabilityOP,
  title={Undefinability of propositional quantifiers in the modal system S4},
  author={Silvio Ghilardi and Marek W. Zawadowski},
  journal={Studia Logica},
  year={1995},
  volume={55},
  pages={259-271}
}