Potamon fluviatile northeastern Greece. In mainland Greece, "P. fluviatile" is found in the drainages of the Axios, Thyamis, Aheron and Arachthos, Pineiós, Piros-Tethreas, Pamisos and Evrotas rivers. In the Ionian Islands, "P. fluviatile" is known to occur at only one site on Corfu, as well as on Kefalonia, Lefkada and Zakynthos. In the Aegean Islands, it is found on Skiathos and Skopelos (Sporades), on Euboea and Skyros, and at a single site on Andros in the Cyclades. "Potamon fluviatile" is at the western distributional limit of the genus "Potamon". Other species in the genus occur through Eastern Europe and the Middle East,
Problem of why there is anything at all that the question cannot have a causal explanation (as any cause must itself have a cause) or a contingent explanation (as the factors giving the contingency must pre-exist), and that if there is an answer it must be something that exists necessarily (i.e. something that just exists, rather than is caused). Gottfried Wilhelm Leibniz wrote: ""Why is there something rather than nothing? The sufficient reason [...] is found in a substance which [...] is a necessary being bearing the reason for its existence within itself."" Philosopher of physics Dean Rickles has argued that numbers and mathematics (or their underlying laws)