function factory( mu ) {
	if ( isnan( mu ) ) {
		return constantFunction( NaN );
	}
	return quantile;

	/**
	* Evaluates the quantile function of a degenerate distribution.
	*
	* @private
	* @param {Probability} p - input value
	* @returns {number} evaluated quantile function
	*
	* @example
	* var y = quantile( 0.5 );
	* // returns <number>
	*/
	function quantile( p ) {
		if ( isnan( p ) || p < 0.0 || p > 1.0 ) {
			return NaN;
		}
		return mu;
	}
}
Returns a function for evaluating the quantile function of a degenerate distribution centered at a provided mean value.

@param {number} mu - value at which to center the distribution
@returns {Function} function to evaluate the quantile function

@example
var quantile = factory( 5.0 );

var y = quantile( 0.3 );
// returns 5.0

y = quantile( 0.1 );
// returns 5.0

y = quantile( 1.1 );
// returns NaN