A great paper on this topic: D. J. Pearce, “Sound and Complete Flow Typing with Unions, Intersections and Negations,” in Verification, Model Checking, and Abst

A great paper on this topic: D. J. Pearce, “Sound and Complete Flow Typing with Unions, Intersections and Negations,” in Verification, Model Checking, and Abstract Interpretation, vol. 7737, R. Giacobazzi, J. Berdine, and I. Mastroeni, Eds. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013, pp. 335–354. doi: 10.1007/978-3-642-35873-9_21. https://ecs.wgtn.ac.nz/foswiki/pub/Main/TechnicalReportSeries/ECSTR12-20.pdf https://ecs.wgtn.ac.nz/foswiki/pub/Main/TechnicalReportSerie...