export function first(set) {
	console.assert(set instanceof Set, set);

	return set.values().next().value;
}



export function last(set) {
	console.assert(set instanceof Set, set);

	let result = undefined;
	for (let value of set.values())
		result = value;
	return result;
}



export function intersection(a, b) {
	console.assert(a instanceof Set, a);
	console.assert(b instanceof Set, b);

	let result = new Set;
	for (let item of a) {
		if (b.has(item))
			result.add(item);
	}
	return result;
}



export function difference(a, b) {
	console.assert(a instanceof Set, a);
	console.assert(b instanceof Set, b);

	let result = new Set;
	for (let item of a) {
		if (!b.has(item))
			result.add(item);
	}
	return result;
}