- $O(n) = \{n, n^{2}, n^{1000000}, 2^{n}, ...\}$ [Source A], [Source B]
- Say $t_{n} \in O(n)$
- By formal definition $t_{n} \leq k \cdot n$ [Source C]
But how can this be? Say $t_{n}$ is actually $n^{2}$, then $t_{n} \leq k \cdot n$ is just false. Would it not be more logical to have $t_{n} \geq k \cdot n$ as a formal definition acompanying $O(n)$?