In Summer of 2020 Alvaro had a backyard pool installed by Bob the builder for $20,000. Alvaro had little money, so Bob agreed to take an assignment of the debt owed to Alvaro by Dodgy Brothers ("Dodgy") as security for the $20,000 owing on the pool. Bob agreed to retransfer the debt to Alvaro as soon as Alvaro had paid him for the pool. Alvaro wrote out an assignment of the debt on a scrappy piece of paper and signed it and gave it to Bob. Two months later, in March 2020 Alvaro decided to give his niece Rose financial help to buy a car. Forgetting that he had assigned Dodgy's debt already, Alvaro said to Rose "You can have half of the debt Dodgy owes me". One month later in May, Alvaro again assigned Dodgy's debt orally to Nathaniel who owned a firm which carried out renovations to Alvaro's home. On the first of December Rose rang Dodgy to tell him of her assignment. The next day Nathaniel did the same. A week later, Bob discovered what Alvaro had done and wrote to Dodgy telling of the assignment and asking Dodgy to pay the debt to him (Bob) as he considered Alvaro to be in default of his obligation to pay for the pool. Alvaro has not yet paid Bob for the pool. Dodgy wants to pay off his debt to Bob but is confused about whom to pay. Advise Dodgy.