Initial Segment of Natural Numbers determined by Zero is Empty
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Theorem
Let $\N_k$ denote the initial segment of the natural numbers determined by $k$:
- $\N_k = \set {0, 1, 2, 3, \ldots, k - 1}$
Then $\N_0 = \O$.
Proof
From the definition of $\N_0$:
- $\N_0 = \set {n \in \N: n < 0}$
From the definition of zero, $0$ is the minimal element of $\N$.
So there is no element $n$ of $\N$ such that $n < 0$.
Thus $\N_0 = \O$.
$\blacksquare$