Symbols:Greek/Delta/Arbitrarily Small Real Number

Arbitrarily Small Strictly Positive Real Number

 * $\delta$

$\delta$ is often used to mean an arbitrarily small (strictly) positive real number.

For example, the definition of a limit of a real function $f$:


 * $\forall \epsilon \in \R_{>0}: \exists \delta \in \R_{>0}: \forall x \in \R: 0 < \size {x - c} < \delta \implies \size {\map f x - L} < \epsilon$

is interpreted to mean:


 * For every arbitrarily small (strictly) positive real number $\epsilon$, there exists an arbitrarily small (strictly) positive real number $\delta$ such that every real number $x \ne c$ in the domain of $f$ within $\delta$ of $c$ has an image within $\epsilon$ of $L$.