Regular Expressions (Rules) Regular expressions over alphabet Reg.Expr Language it denotes 8 {ε} a∈∑ {a} ()|(2) L()UL(2) (1)(2) L(r1)L(2) (r) (L(r) (r) Lr) ·(r)=(r)r)* ·(r)?=()|E CS308 Compiler Theory 9Regular Expressions (Rules) Regular expressions over alphabet Σ Reg. Expr Language it denotes ε { ε } a∈ Σ {a} (r ) | (r ) L(r ) ∪ L(r ) 1) | (r 2 ) L(r1) ∪ L(r 2 ) (r1) (r 2) L(r1) L(r 2 ) (r) * (L(r)) * (r) L(r) • (r) + = (r)(r) * • ( r )? = ( r ) | ε 9 ( ) ()| CS308 Compiler Theory