# Ullman (Compiler Design) Edition 2 Exercise 3.3 Question 2 (Page No. 125)

339 views

Describe the languages denoted by the following regular expressions:

1. $a(a\mid b)^{\ast}a.$
2. $((\epsilon\mid a)b^{\ast})^{\ast}.$
3. $(a\mid b)^{\ast}a(a\mid b)(a\mid b).$
4. $a^{\ast}ba^{\ast}ba^{\ast}ba^{\ast}.$
5. $(aa\mid bb)^{\ast}((ab\mid ba)(aa\mid bb)^{\ast}(ab\mid ba)(aa\mid bb)^{\ast})^{\ast}.$

a). start and end with a.

b). (a+b)* or we can say universal set on symbols (a,b).

c). end with aaa or aab or aba or abb.

d). containing exactly 3 b's.

e). m solving (i will post (e) asap.)

correct me if wrong..
1
can we describe c) as third last symbola a
0

e). even no of a’s and b’s.

## Related questions

1
320 views
Most languages are case sensitive, so keywords can be written only one way, and the regular expressions describing their lexeme is very simple. However, some languages, like SQL, are case insensitive, so a keyword can be written either in lowercase or in ... regular expression for a keyword in a case-insensitive language. Illustrate the idea by writing the expression for "select" in SQL.
2
545 views
Write regular definitions for the following languages: All strings of lowercase letters that contain the five vowels in order. All strings of lowercase letters in which the letters are in ascending lexicographic order. Comments, consisting of a string surrounded by /* and */, without ... 's that do not contain the substring abb. All strings of a's and b's that do not contain the subsequence abb.
1 vote
3
153 views
In a string of length $n$, how many of the following are there? Prefixes. Suffixes. Proper prefixes. Substrings. Subsequences.