# Symbols:Q

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### Set of Rational Numbers

$\Q$

The set of rational numbers.

The $\LaTeX$ code for $\Q$ is \Q  or \mathbb Q or \Bbb Q.

### Set of Non-Zero Rational Numbers

$\Q_{\ne 0}$
$\Q_{\ne 0} = \Q \setminus \left\{{0}\right\}$

The $\LaTeX$ code for $\Q_{\ne 0}$ is \Q_{\ne 0}  or \mathbb Q_{\ne 0} or \Bbb Q_{\ne 0}.

### Set of Non-Negative Rational Numbers

$\Q_{\ge 0}$
$\Q_{\ge 0} = \set {x \in \Q: x \ge 0}$

The $\LaTeX$ code for $\Q_{\ge 0}$ is \Q_{\ge 0}  or \mathbb Q_{\ge 0} or \Bbb Q_{\ge 0}.

### Set of Strictly Positive Rational Numbers

$\Q_{> 0}$
$\Q_{> 0} = \set {x \in \Q: x > 0}$

The $\LaTeX$ code for $\Q_{> 0}$ is \Q_{> 0}  or \mathbb Q_{> 0} or \Bbb Q_{> 0}.

### Probability

$q$

Used in conjunction with the general probability $p$:

$q = 1 - p$

As such, $q$ is a real number such that:

$0 \le q \le 1$

and

$p + q = 1$

The $\LaTeX$ code for $q$ is q .

### Quotient Mapping

$q_\RR$
$q_\RR: S \to S / \RR: \map {q_\RR} s = \eqclass s {\RR}$

where:

$\RR \subseteq S \times S$ be an equivalence relation on a set $S$
$\eqclass s \RR$ is the $\RR$-equivalence class of $s$
$S / \RR$ is the quotient set of $S$ determined by $\RR$.

Also known as:

the canonical surjection from $S$ to $S / \RR$
the canonical map or canonical projection from $S$ onto $S / \RR$
the natural mapping from $S$ to $S / \RR$
the natural surjection from $S$ to $S / \RR$
the classifying map or classifying mapping (as it classifies the elements of $S$ into those various equivalence classes)
the projection from $S$ to $S / \RR$

The $\LaTeX$ code for $q_\RR: S \to S / \RR$ is q_\RR: S \to S / \RR .

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