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/** * **reduce** applies a reductor function to all elements of the array while * keeping the aggragete of previous iterations; returns a single value * @param fn a reductor function * @param def default value * @param xs input array * @returns a single element (the aggregate/accumulator) */export default function reduce<T, R>(fn: (aggr: R, x: T) => R, def: R, xs: T[]): R {    return xs.reduce(fn, def);}