**SCAN Expressions**

There are two types of SCAN expressions

the simple one:

wt=L1n1#L2n2...#Ltnt

and the complex one:

wt=L1n1#[List1]L2n2...#[Listt-1]Ltnt

Where t stands for the length of the SCAN expression wt, t in Z+.

Li is a SCAN letter, ni is a power of 2, i in {1,...t}.

[Listi] are lists such as: (l1,m1)...(lr,mr) where r = n1*...ni