Week 9

Language is introduced today with several methods associated with it. We start by defining strings. Though we have been using it quite frequently but we rarely really stick into it. Alphabet is introduced as well, this one is not the same one in English. Sigma, which used to denote summation, is used to denote Alphabet here. Just like the Alphabet in English, the Alphabet we are talking about also contains all the candidate that are waiting to be choosing and combining to form different strings. All the possible combination will be Sigma*. There are several manipulating options for strings as well, for example you can concatenate two strings into one, take the length of the string, make a reverse of a string, or take nth power of a string. Beyond a string we have another concept called language, and it's not a nature language we are talking about. The language is formed from sigma. So we can certainly make a union or interaction of two languages, make a copy of concatenation of the two, and the most important Kleene star. The Kleene star is all the possible concatenation of the two language. After that we talked about the regular expression. I have never ever heard regular expression before so it really took a while for me to become comfortable with it. I looked up it on the wiki, and figured out what "*" and "+" means. Since this is essential for CSC207 as well, I will definitely do more exercises with the regular expression.