/**
 * Unit-quaternion helpers for the per-factor arithmetic of Rotor4
 * animation. Layout matches Rotor4's factors: [i, j, k, real] — the
 * real part lives at index 3 so a quaternion doubles as a 4D point.
 *
 * None of these choose a double-cover sign: on SO(4) the cover choice
 * is a *pair-level* decision ((l, r) ~ (−l, −r) only jointly), so it is
 * made once, by the track's neighborhooding pass, never inside factor
 * arithmetic.
 */
export declare function qdot(a: Float64Array, b: Float64Array): number;
export declare function qmul(a: Float64Array, b: Float64Array): Float64Array;
export declare function qconj(a: Float64Array): Float64Array;
export declare function qnormalize(a: Float64Array): Float64Array;
/**
 * Log of a unit quaternion: the pure-imaginary [v·θ̂, 0] with θ the
 * rotation half-angle. atan2 form — accurate near identity where
 * acos(w) loses digits, and well-defined at θ = π/2 (w = 0). Only
 * q → −1 is singular, which neighborhooded tracks never approach.
 */
export declare function qlog(a: Float64Array): Float64Array;
/** Exp of a pure-imaginary quaternion (inverse of qlog). */
export declare function qexp(v: Float64Array): Float64Array;
/**
 * Geodesic interpolation toward `b` as stored — no shortest-arc flip
 * (see module note). Falls back to nlerp for nearly parallel inputs.
 */
export declare function qslerp(a: Float64Array, b: Float64Array, t: number): Float64Array;
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