We thank A. Naimark for the following example.

Consider the bank accounts of two people; they contain different cuurencies, like NIS, US $ , and so on. If these two people want to make with these accounts one single joint account, the resulting NIS position will be the sum of their respective NIS positions, the resulting US $ position will be the sum of their respective US $ positions, and so on.

By the same way, suppose that the director of a branch of a certain bank decided to grant the owner of a specific account a special bonus of 2 percent. In order to know what is the new position in every currency, we have to multiply each entry in the account position by 1.02.

An example is given in the following table.

These examples, together with others, explain why we are interested in the following section.