function Set() {

	var items = {};

	this.has = function(value) {

		return value in items

	}

	this.add = function(value) {

		if (!this.has(value)) {

			items[value] = value;

			return true

		}

		return false

	}

	this.remove = function() {

		if (this.has(value)) {

			delete items[value];

			return true

		}

		return false

	}

	this.size = function() {

		return Object.keys(items).length

	}

	this.values = function() {

		return Object.keys(items)

	}

	this.union = function(otherSet) {

		var unionSet = new Set();

		var values = this.values();

		for (var i = 0; i < values.length; i++) {

			unionSet.add(values[i])

		}

		values = otherSet.values();

		for (var i = 0; i < values.length; i++) {

			unionSet.add(values[i])

		}

		return unionSet

	}

	this.intersection = function(otherSet) {

		var intersection = new Set();

		var values = this.values();

		for (var i = 0; i < values.length; i++) {

			if (otherSet.has(values[i])) {

				intersection.add(values[i])

			}

		}

		return intersection

	}

	this.difference = function(otherSet) {

		var differece = new Set();

		var values = this.values();

		for (var i = 0; i < values.length; i++) {

			if (!otherSet.has(values[i])) {

				differece.add(values[i])

			}

		}

		return differece

	}

	this.subSet = function(otherSet) {

		var subSet = new Set();

		if (this.size() > otherSet.size()) {

			return false

		}

		var values = this.values();

		for (var i = 0; values.length; i++) {

			if (!otherSet.has(values[i])) {

				return false

			}

		}

		return true

	}

}