Let A={a,b}. So the question is to write regular expression such that L(r) which consists of all words.
My answer is this:
L(r)= (a+b)* a* b* (a+b)*
Is this correct?
Also another solution is:
L(r)=(a+b)*
Is this correct?
Is (a+b)* same as (a,b)* ?
Is (a+b)* same as (a,b)* ?
Close, but try not to mix domains. If the regular expression $r$ is the string $(a{+}b)*$, then the language of $r$ is the set of all strings over $\{a,b\}$, or $L(r) = \{a,b\}^*$.
So, $(a{+}b)*$ and $\{a,b\}^*$ denote the same set of strings. The first one as regular expression, the second one in set notation.
