 Let's take a look at how we use the four basic symbols in a regular expression, starting with the parentheses. In arithmetic, if we have the equation 1 plus 2 times 3, we follow the order of arithmetic expressions and solve the multiplication first, so we get 1 plus 6, which equals 7. But if we add parentheses around 1 plus 2, it holds the highest precedence, and so we get 3 times 3, which equals 9. In rejects, parentheses work in the same way, specifying the highest precedence. Next we have the clean star, named after the man who helped found the concept of regular expressions. This matches the preceding symbol repeated zero or more times. For example, B A star will match B and B A and B A A and B A A A and so on. Lastly, we have the alternation symbol. This can be read as a choice, so the expression A parentheses A bar B parentheses matches both A A and A B. We usually refer to this as bar and read it as or. Bar has the lowest precedence of the basic reject symbols, so A or B star is the same as saying A or B star, which means you can either match an A or any number of B's.