Apply the Account/Transaction pattern to the parallel financial transactions of the example shown in Figs. 11–31 to 11–35. As the bills may be paid forward, it may be necessary to use memo entries. Define the set of instances of Account and Transaction that are necessary and describe them.

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Account | < > +name: String + / balance: Integer = movement->sum(value) Movement +value: Integer INSTANCES Account name = "supplier" balance = 0 Account name = "pending orders" balance = 0 Account name = 'stock" balance = 0 Account name = "sold" balance = 0 :Account name = "delivered" balance = 0 2 1 Transaction {movement->sum(value) = 0} < > +name: String FIGURE 11-31 Initial state of an accounting system for products.