import type { ArrayVector4D } from "./types.js";
/**
 * Calculates the angle between a 4D vector and the positive y-axis.
 * @param {ArrayVector4D} xyzw - Vector as `[x, y, z, w]`
 * @returns {number} The angle in radians
 */
export declare const angleY4D: (xyzw: ArrayVector4D) => number;