Trading is where you back or lay an outcome in anticipation of a change in the odds that will allow a further bet to guarantee a profit. For example, at the start of the season, a punter backs Liverpool to win the Premiership at odds of 15.0 with a stake of £100. As the season progresses, Liverpool’s form is such that the odds shorten to 4.0. The punter now lays Liverpool at these odds to win £150, thereby guaranteeing a profit regardless of the outcome of the Premiership. If Liverpool win the league, the payout is £900 (profit from back bet minus liability from lay bet: £1500 – £600). If Liverpool fail to win the league, the payout is £50 (profit from lay bet minus back bet stake, £150 – £100). The former, more profitable, outcome is more favourable, but the punter will not lose money either way. A combination of bets that guarantees a profit is known as a green book.