I´ve been calling the horizon of the concrete that line that divides properties from objects. (In my square representation, properties are in the northern hemisphere in the universal and abstract corners while objects are south in the particular and concrete corners). Abstract things - like mathematical items or properties or even tropes - are such that the Leibniz law (that claims both that the identicals are indiscernible and that the indiscernibles are identical) holds. Leibniz, as a radical bundle theorist, takes it to hold all the way. There is no concrete, no horizon of the concrete. All items belong to the abstract hemisphere and their particularity satisfies Leibniz law. Leibniz finds a way to get rid of all concretude, it is the basis of a mathesis universalis.
To invert Leibniz up side down could be to consider no more than the side of concretude; to allow for no abstracta where the Law is satisfied. No indiscernible is identical and no identical is indiscernible. There is no principle of reason (maybe rather something akin to the principle of unreason put forward bu Meillassoux) or maybe no principle whatsoever. There is no more than history, the history of the processes of individuation. Only things being treated as individuals in a specific region of the process. This amounts to say that contingency is the mark of the natural. And the concrete is the harbour of contingency. But I suspect there are other ways to think about the concrete that finds alternative ways to keep the horizon of the concrete instead of dissolving it.