Post completeness in a logical system means that adding any new axiom not already derivable collapses the system into triviality, making it a maximally consistent logic. For classical propositional logic, the Post-complete extensions are fully understood, but for conditional logics built around counterfactual reasoning, such as Lewis's family of sphere-semantics systems, the landscape of Post-complete extensions remains poorly mapped. The open problem is to find a complete and computable classification of all Post-complete logics extending standard conditional systems like VC, ideally expressed through properties of the Lewisian sphere models or through algebraic structures analogous to Boolean algebras.