Legal tender is a narrow technical concept for the settlement of debt, and it has little practical meaning for many everyday transactions such as buying goods in shops. But it does apply, for example, to the settlement of a restaurant bill, where the food has been eaten prior to demand for payment and so a debt exists. Essentially, any two parties can agree to any item of value as a medium for exchange when making a purchase (in that sense, all money is ultimately an extended form of barter). If a debt exists that is legally enforceable and the debtor party offers to pay with some item that is not legal tender, the creditor may refuse such payment and declare that the debtor is in default of payment; if the debtor offers payment in legal tender, the creditor is required to accept it or else the creditor is in breach of contract. Thus, if in England party A owes party B 1,000 pounds sterling and offers to pay in Northern Irish banknotes, party B may refuse and sue party A for non-payment; if party A provides Bank of England notes, party B must acknowledge the debt as legally paid even if party B would prefer some other form of payment.