...denote an element of a sequence by (xi, x%, . . . , xm), where Xj is an item. An item can occur only once in an element of a sequence, but can occur multiple times in different elements. An itemset is considered to be a sequence with a single element. A sequence < a\a.2 • • • an...

...xm), where x/t is an item. For brevity, the brackets are omitted if an element has only one item, ie, element (x) is written as x. An item can occur at...elements of a sequence. The number of instances of items in a sequence is called the length of the sequence. A sequence with length / is called an /-sequence....