mult(x, y, _id) {
        let id = this._tsid(_id, `mult`)
        let x0 = this.na(x) ? NaN : (x.__id__ ? x[0] : x)
        let y0 = this.na(y)? NaN : (y.__id__ ? y[0] : y)
        return this.ts(x0 * y0, id, x.__tf__)
    }
Multiplies values / time-series
@param {(TS|*)} x - First input
@param {(TS|*)} y - Second input
@return {TS} - New time-series