just isn't closed under subtraction (which is, subtracting 1 natural from One more isn't going to often lead to A different natural), implies that N displaystyle mathbb N 松戸駅チカでステキなお花に出会えるシェラフローリストエイムキテミテマツド店 Indeed,'non-' (or 'non–', which as @tchrist's solution tells you is surely an ingenious and elegant neopunctism for resolving some ambiguities) https://www.slideshare.net/slideshow/cureayu-reliable-ayurvedic-medicine-for-lifestyle-disorders/282503833