Use the PhotoDB schema to answer this question. Provide a relational algebra query that gives a list of names (both first and last) of any users in the system not tagged in the pictures.

PhotoDB is a database for a simple photo sharing web application that allows users to upload photos and tag other users in each photo. It consists of four tables: 1. Users - users of the system. 2. Cameras - basic information about the various cameras used to take photos. Note that a camera is only related to pictures, not to an owner. 3. Pictures - the pictures being stored in the system. a. The location attribute is a user-entered value intended to store the geographical location where the picture was taken... "Boston, MA" or "Paris", for example. 4. Tags - contains information about which users have been tagged in photos. a. A person cannot be tagged in a photo if they aren't already a user in the system