# Tagged Questions

Regular expressions or Regex is a search pattern for strings defined by a sequence of characters.

97 views

### Regular expression 00 or 11 not both

Can anyone help me with this question: I know it before, but I have tried to solve it myself and didnt succeed. what is the regular expression for this language: L=all words that have 00 or 11 but not ...
367 views

### Converting from NFA to a regular expression.

This is a NFA, I have been working to covert it to a regular expression. After I'am done, I arrive at an expression as follows  \left(((a\cup b)a^*b) (ba^*b)^*a\right)^* \left(((a\cup b)a^*b) (ba^...
93 views

57 views

### Drawing automata for languages

I'm trying to draw two automata for these two languages: For the first one, I know that the minimum is n = 1, m = 1, but I'm having troubles drawing a NFA for it. The second one the minimum is n = ...
39 views

### Is $L_1$ context free language?

Let $L = L_1 \cap L_2$, where $L_1$ and $L_2$ are languages as defined below: $L_1= \left \{ a^m b^mca^nb^m \mid m,n \geq 0 \right \}$ $L_2=\left \{ a^i b^j c^k \mid i,j,k \geq 0 \right \}$ Then L ...
467 views

### A regular expression for the words that don't contain the sequence $ab$ over $\{a,b,c\}$

The following is an exercise in a book I am reading: Let $\Sigma=\{a,b,c\}$, define $L$ to be the language of all words over $\Sigma$ that do not contain $ab$ as a sub-word. Find a regular ...
117 views

### Number of sequences that contain a given “run”

Consider sequences of numbers 0, 1, 2 with length n. There are $3^n$ such sequences. I want to know how many sequences there are that contain a k-run of 1's followed by 2. As a regular expression: ...