function ibetaSeriesT( a, b, x, result ) {
	var poch = 1.0 - b;
	var n = 1;
	return next;

	/**
	* Calculate the next term of the series.
	*
	* @private
	* @returns {number} series expansion term
	*/
	function next() {
		var r = result / a;
		a += 1.0;
		result *= poch * x / n;
		n += 1;
		poch += 1.0;
		return r;
	}
}
Series approximation to the incomplete beta.

@private
@param {NonNegativeNumber} a - function parameter
@param {NonNegativeNumber} b - function parameter
@param {Probability} x - function parameter
@param {number} result - initial result value
@returns {Function} series function