# regular expression with kleene closure [duplicate]

• Essentially $1^*$ means "any word consisting of any (finite) number of ones". If R is a RE and L(R) is its language, then R^* is "any word consisting of the concatenation of any (finite) number of words in L(R)". For example if $R = a+b$ then $R^*$ contains the word "abba" as it is the concatenation of "a", "b", "b", and "a", all of which are in $L(R) = \{a, b\}$. Going back to your case, you have $R = 1^*$ so $R^* = (1^*)^*$ is "any word obtained by concatenating any (finite) number of words containing only ones"... a convoluted way to say "any word containing only ones". – Steven Jun 29 at 0:21