`   == How is this true ==  ``An immediate consequence of Extensionality is that no two atoms can be identical.``  Extensionality is about parthood, not about Leibniz law and the properties they have. That would be to prove for all x and all y if Fx iff Fy then x = y. But how does this follow from Extensionality? The consequence should be that no two atoms can share all their proper parts.  `