I don't see what the question is..
Here is the homework problem I am having:
Let A be the set of lower case letters ({a,b,c,...,z}), and for each integer i between 1 and 9 inclusive, let Si be the set of strings s1, s2, ...s10 of length 10 over A such that si comes later in the alphabet than si+1 and for every j and for every k such that j does not equal k and sj does not equal sk
(so I am learning how to use LATEX and I do not know how to do subscript. Please note that the italic variables and numbers after the regular variables are supposed to be in subscript)
here is the question I am struggling with
I need to give an example of an element of (S4 S3)-S7