Regular expressions

  Got my test 2 back, it's pretty good as expected :)
  We just encountered regular expressions in CSC236, it also appears in 207, so it's good for me to learn it in both courses, but actually I've heard it in CSC148 or 108 can't remember exactly.
  For CSC236, it's more focused on binary strings, in that case, we can simply connect RegEx with finite state automata, but I'm pretty sure that in future we are gonna face some problems that involve letter and number combined cases, can't just be this simple.
  And the next tutorial is about how to devise and prove a regular expression that satisfies the given conditions, of course, the base case comes first which should pass the empty case, empty string case, and one-symbol string case, then for the induction step, we need to show that if R and S belongs to a set, then (R+S), RS and R* should all belong to the set.