Answer:
No. Then the automaton would accept strings that start with any number of 'a'.
No. Then the automaton would accept strings that start with any number of 'a'.
Rule 6. ZERO or More Instances
The character * in a regular expression
means "match the preceding character zero or many times".
For example A* matches any number (including zero) of
character 'A'.
| Regular Expression | Matches |
|---|---|
a* | ZERO or more 'a' |
ba* | b, ba, baa, baaa, baaaa, ... |
[ab]* | Ø, a, ab, aaa, ababb, bbb, ... zero or more characters, each character an 'a' or 'b' |
[^0-9]* | Ø, A, ABC, zw$nn, ... zero or more characters, no character a digit |
a*b* | Ø, a, aaa, aaab, abbb, b, bbb, ... zero or more 'a', followed by zero or more 'b' |
In the above, Ø is the "empty string" — the string containing no characters. This sounds odd, but it is like a bank account with no money. It is useful to talk about the account, even it it is empty.
Stephen Kleene (1909-1994) was one of the early investigators of regular expressions and finite automata. The "Kleene star" is often used in computer science. It is a phrase you should know. Kleene pronounced his name "klay-nee", but often people pronounce it "klee-nee".
Does [fr]*og match "frog" ?