 The second principle, (P.4b), is stronger: it rules out both models as unacceptable. However, (P.4b) is still too weak to capture the intended idea. For example, it is satisfied by a model in which a whole can be decomposed into several proper parts all of which overlap one another (Figure 2, right), and it may be argued that such models do not do justice to the meaning of ‘proper part’: after all, the idea is that the removal of a proper part should leave a remainder, but it is by no means clear what would be left of x once z (along with its parts) is removed.