function merge_tables(this_table, other_table) {
	const new_table = this_table.slice();
	const idx_map = [];
	other_table = other_table || [];
	let val_changed = false;
	for (const [other_idx, other_val] of other_table.entries()) {
		const this_idx = this_table.indexOf(other_val);
		if (this_idx >= 0) {
			idx_map[other_idx] = this_idx;
		} else {
			const new_idx = new_table.length;
			new_table[new_idx] = other_val;
			idx_map[other_idx] = new_idx;
			val_changed = true;
		}
	}
	let idx_changed = val_changed;
	if (val_changed) {
		if (idx_map.find((val, idx) => val != idx) === undefined) {
			// idx_map is identity map [0, 1, 2, 3, 4, ....]
			idx_changed = false;
		}
	}
	return [new_table, idx_map, val_changed, idx_changed];
}
@template T
@param {T[]} this_table
@param {T[]} other_table
@returns {[T[], number[], boolean, boolean]}