code: function(){
  		return underscore.reduce(arguments, function(first, second){
  			return underscore.union(
  				underscore.difference(first, second),
  				underscore.difference(second, first)
  			);
  		});
  	}
docs: ### symmetricDifference*(set1, set2[, ...setN])* The symmetric of two sets is is the set of elements in either set, but not their intersection. If two sets are equal, the symmetric difference is empty.