Symbols:Greek/Epsilon

Element of a Set

 * $$x \in S$$, $$S \ni x$$

See element of a set.

The LaTeX code for $$\in$$ is \in.

The LaTeX code for $$\ni$$ is \ni (that is, "in" backwards).

A small positive quantity
Many a proof in analysis will famously start:
 * "Let $$\epsilon > 0$$ ..."

where it is frequently left unstated that $$\epsilon$$ is a real number, arbitrarily small.

The LaTeX code for $$\epsilon > 0$$ is \epsilon > 0.

Alternative Symbol
While $$\epsilon$$ is common, so is $$\varepsilon$$. The symbols are, in general, interchangeable.

Some writers prefer $$\epsilon$$ and some prefer $$\varepsilon$$.

The LaTeX code for $$\varepsilon$$ is \varepsilon.