Free constructions and coproducts of d-framesTomás Jakl, Achim JungArXiv2017A general theory of presentations for d-frames does not yet exist. We review the difficulties and give sufficient conditions for when they can be overcome. As an application we prove that the category of d-frames is closed under coproducts.
Bitopology and Four-valued LogicTomás Jakl, Achim Jung, Ales PultrElectr. Notes Theor. Comput. Sci.2016