/**
 * The circle constant **τ** (tau), equal to **2π** `(≈ 6.283185307179586)`.
 * Useful for full rotations, radians-per-turn calculations, angular velocity,
 * and other periodic math where factors of 2 arise naturally.
 *
 * $$
 * \tau = 2\pi
 * $$
 * $$
 * 1\ \text{turn} = \tau\ \text{radians} = 360^\circ
 * $$
 * $$
 * \theta_{\text{rad}} = t\,\tau \quad (\text{turn fraction } t \in [0,1))
 * $$
 * $$
 * \theta_{\deg} = \frac{180^\circ}{\pi}\,\theta_{\text{rad}} = 360^\circ\,t
 * $$
 * $$
 * \omega = 2\pi f = \tau f \quad\text{(angular frequency)}
 * $$
 * $$
 * T = \frac{2\pi}{\omega} = \frac{\tau}{\omega} \quad\text{(period)}
 * $$
 *
 * @readonly
 *
 * ::: info
 *
 * - Using **τ** often simplifies formulas that involve *full cycles* (e.g., Fourier analysis,
 *   rotations, oscillator phase), eliminating stray factors of 2.
 * - `TWO_PI` is a runtime numeric constant; do not compare floating-point results using `===`
 *   when they involve trigonometric operations-prefer tolerance checks.
 *
 * :::
 *
 * @see https://en.wikipedia.org/wiki/Tau_(mathematics)
 * @see https://en.wikipedia.org/wiki/Radian
 *
 * @example
 * ```ts
 * import { TWO_PI } from "./constants";
 *
 * // A quarter turn (π/2 radians)
 * const quarterTurn = 0.25 * TWO_PI; // ≈ 1.5707963267948966
 *
 * // Point on the unit circle at 1/8 of a turn
 * const t = 1 / 8;
 * const angle = t * TWO_PI;  // τ/8 = π/4
 * const x = Math.cos(angle); // ≈ 0.7071
 * const y = Math.sin(angle); // ≈ 0.7071
 * ```
 *
 * @example
 * ```ts
 * // Wrap any angle (radians) to [0, τ):
 * function wrapTau(theta: number): number {
 *   const tau = TWO_PI;
 *   return ((theta % tau) + tau) % tau;
 * }
 *
 * // Convert turn fraction to radians:
 * const radiansFromTurns = (turns: number) => turns * TWO_PI;
 *
 * // Angular frequency from frequency (Hz):
 * const omega = (f: number) => TWO_PI * f; // ω = τ f
 * ```
 * @group Math
 */
export declare const TWO_PI: number;
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