function factory( mu, sigma ) {
	var A;
	var B;
	if ( isnan( mu ) || isnan( sigma ) || sigma < 0.0 ) {
		return constantFunction( NaN );
	}
	if ( sigma === 0.0 ) {
		degenerate( mu );
	}
	A = mu;
	B = sigma * sqrt( 2.0 );
	return quantile;

	/**
	* Evaluates the quantile function for a normal distribution.
	*
	* @private
	* @param {Probability} p - input value
	* @returns {number} evaluated quantile function
	*
	* @example
	* var y = quantile( 0.3 );
	* // returns <number>
	*/
	function quantile( p ) {
		if ( isnan( p ) || p < 0.0 || p > 1.0 ) {
			return NaN;
		}
		return A + ( B * erfinv( (2.0*p) - 1.0 ) );
	}
}
Returns a function for evaluating the quantile function of a normal distribution.

@param {number} mu - mean
@param {NonNegativeNumber} sigma - standard deviation
@returns {Function} quantile function

@example
var quantile = factory( 10.0, 2.0 );
var y = quantile( 0.5 );
// returns 10.0

y = quantile( 0.8 );
// returns ~11.683