function factory( x0, gamma ) {
	if (
		isnan( x0 ) ||
		isnan( gamma ) ||
		gamma <= 0
	) {
		return constantFunction( NaN );
	}
	return quantile;

	/**
	* Evaluates the quantile function for a Cauchy 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 x0 + ( gamma * tan( PI*( p-0.5 ) ) );
	}
}
Returns a function for evaluating the quantile function for a Cauchy distribution with location parameter `x0` and scale parameter `gamma`.

@param {number} x0 - location parameter
@param {PositiveNumber} gamma - scale parameter
@returns {Function} quantile function

@example
var quantile = factory( 10.0, 2.0 );
var y = quantile( 0.2 );
// returns ~7.247

y = quantile( 0.8 );
// returns ~12.753