Here is the homework problem I am having:

LetAbe the set of lower case letters ({a,b,c,...,z}), and for each integeribetween 1 and 9 inclusive, letSibe the set of strings s1, s2, ...s10 of length 10 overAsuch that sicomes later in the alphabet than si+1and for every j and for every k such that j does not equal k and sjdoes 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 (S4S3)-S7