# Tag Info

Accepted

### DFA and NFA with 2 Substrings

Find an automaton for $L_1= \{uopv\mid u,v\in \Sigma^*\}$ and an automaton for $L_2 = \{upqv\mid u,v\in\Sigma^*\}$ (this should be easy enough). Then, you can compute the product automaton of the two ...
• 7,107

### regex find substring matches in text

One approach is to match against the regexp .* E .*, then figure out how it matches. Whether you can figure out how that matched depends on the algorithm you are ...
• 141k

### Showing that $(b^*a)^+.(b^*a) = (b^*a)^*$

let A=(b* a)+ ,B=(b* a) and C=(b* a)* we have to show that whether A.B=C here . indicates the concatenation of strings '+' is known as Kleene plus which means all kinds of non empty strings are ...

### Construct a regular expression for the set of strings over {a, b} that contain an odd number of a's and at most four b's

It says the constraints are Odd number of A's and At most 4 B's let's start the expression ->string may start with both A & B ======>(A+B) ->say the first letter of the string be A =====...
1 vote
Accepted

### Why is $L'=\{u\#v^R ~|~ u,v \in L\}$ and $L\in RL$ a regular language?

Regular languages are closed under reversal, therefore $L^R = \{v^R \mid v \in L\}$ is regular. Moreover, regular languages are closed under concatenation, therefore $L' = L \circ \{\#\} \circ L^R$ is ...
• 23.4k

### Regular Expressions with at least 3 b's and at most 2 a's

A regular expression can be developed from the following finite state machine for at most 2 As and at least 3 Bs by using all possible paths separate by |, and using * where their is a loop edge. ...
• 217
Accepted

### Are the set of all Bitcoin addresses a context-sensitive language?

Any answer I give you is likely to be unsatisfying and a little silly, both because we're squarely in theory-land here (and not the useful kind of theory, but theory that is irrelevant in practice), ...
• 141k