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Simons pro LP (Locke s principle, weak) - for substances: No two can be at the same place at the same time.
Falsehood principles / modal mereology / Kit Fine: in a possible world, where an object does not exist, every sentence is wrong, that says that this object has a part or is a part of something (not without truth value). - This also applies to overlapping, but not to separateness. - Def weakly separated / Simons: are objects when in a possible world either both exist or both do not exist there. - Def strongly separated / Simons: here one might demand, that the objects exist in a possible world in which they are separated. - This is just contrary, not contradictory to overlap. -> part-of-relation.
Parts Oxford New York 1987