Transaction T asks to write an item (x) whose value has already been written by a
younger transaction, that is ts(T) < write_timestamp(x). This means that a later trans-action has already updated the value of the item, and the value that the older trans-action is writing must be based on an obsolete value of the item. In this case, the write operation can safely be ignored. This is sometimes known as the ignore obsolete
write rule, and allows greater concurrency.