Real Number is between Ceiling Functions
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Theorem
- $\forall x \in \R: \ceiling {x - 1} \le x < \ceiling x$
where $\ceiling x$ is the ceiling of $x$.
Proof
$\ceiling x$ is defined as:
- $\ceiling x = \map \inf {\set {m \in \Z: m \ge x} }$
So $\ceiling x \ge x$ by definition.
Now $\ceiling {x - 1} < \ceiling x$, so by the definition of the infimum:
- $\ceiling {x - 1} > x$
The result follows.
$\blacksquare$