The main contents of this chapter include all of the following: Intersection of two regular languages is regular, examples, non regular language, example. | Lecture note Theory of automata - Lecture 25 Lecture 1 Theory Of Automata By Dr. MM Alam Text and Reference Material 1. Introduction to Computer Theory by Daniel I. Cohen John Wiley and Sons Inc. 1991 Second Edition as a Text Book 2. Introduction to Languages and Theory of Computation by J. C. Martin McGraw Hill Book Co. 1997 Second Edition for Additional Reading What does Theory of automata mean The word Theory means that this subject is a more mathematical subject and less practical. It is not like your other courses such as programming. However this subject is the foundation for many other practical subjects. Automata is the plural of the word Automaton which means self-acting In general this subject focuses on the Theory of Automa Applications This subject plays a major role in Theory of Computation Compiler Construction Parsing Formal Verification Defining computer languages Types of languages There are two types of languages Formal Languages are used as a basis for defining computer languages A predefined set of symbols and string Formal language theory studies purely syntactical aspects of a language . word abcd Informal Languages such as English has many different versions. Basic Element of a Formal Language Alphabets Definition A finite non-empty set of symbols letters is called an alphabet. It is denoted by Greek letter sigma Σ. Example Σ 1 2 3 Σ 0 1 Binary digits Σ i j k Example Computer Languages C Language Java Language C Java Visual C What are Strings A String is formed by combining various symbols from an alphabet. Example If Σ 1 0 then 0 1 110011 . Similarly If Σ a b then a b abbbbbb aaaabbbbb . What is an EMPTY or NULL String A string with no symbol is denoted by Small Greek letter Lambda λ or Capital Greek letter Lambda Λ. It is called an empty string or null string. We will prefer Λ in this course. Please don t confuse it with logical operator and . One important thing to note is that we never allow Λ to be part of alphabet of a language .
