/**
 * Calculates the proportional value of `x`, `y`, and `z` in a ratio.
 *
 * @param x - The first value in the ratio.
 * @param y - The second value in the ratio.
 * @param z - The third value in the ratio.
 * @param which - If set to `true`, x : y = z : ?. Otherwise, x : y = ? : z
 *
 *@example
 *console.log(Ump.PropRatio(4, 2, 1, false)) // 2
 *@exmaple
 *console.log(Ump.PropRatio(4, 2, 1, true)) // 0.5
 *
 */
export declare function propRatio(x: number, y: number, z: number, which?: boolean): number;