return {
	make: make,
	vertical: vertical,
	horizontal: horizontal,
	diagonal: diagonal,
	zero: zero,
	plus: plus,
	opposite: opposite,
	isSmaller: isSmaller,
	key: key,
	ofKey: ofKey
};

function make(row, column) {
	return {row: row, column: column};
}

function zero() {
	return make(0, 0);
}

function vertical(length) {
	return make(length, 0);
}

function horizontal(length) {
	return make(0, length);
}

function diagonal(length) {
	return make(length, length);
}

function plus(v0, v1) {
	return {row: v0.row + v1.row, column: v0.column + v1.column};
}

function opposite(v) {
	return {row: -v.row, column: -v.column};
}

function isSmaller(v0, v1) {
	return v0.row <= v1.row && v0.column <= v1.column;
}

function key(v) {
	return v.row + ':' + v.column;
}

function ofKey(k) {
	return make.apply(null, k.split(':'));
}