Summary Introduction to the course title, Formal and In-formal languages, Alphabets, Strings, Null string, Words, Validand In-valid alphabets, length of a string, Reverse of a string, Defining languages, Descriptive definition of languages, EQUAL, EVEN-EVEN, INTEGER, EVEN, { a n b n }, { a n b n a n }, factorial, FACTORIAL, DOUBLEFACTORIAL, SQUARE, DOUBLESQUARE, PRIME, PALINDROME. What does automata mean? Definition : It is the plural of automaton, and it means “something that works automatically” Introduction to languages There are two types of languages 1) Formal Languages (Syntactic languages) 2) Informal Languages (Semantic languages) Alphabets Definition : A finite non-empty set of symbols (called letters), is called an alphabet. It is denoted by Σ ( Greek letter sigma). Example Σ = {a,b} Σ = {0,1} (important as this is the language which the computer understands.) Σ = {i,j,k} Note Certain version of language AL