Unit 9 - Regular Expressions

Question 1

Regex Notation: ∅

Answer 1

Empty regex

no word

Question 2

Regex Notation: ε

Answer 2

Empty word

the empty word ε

Question 3

Regex Notation: b (if b∈Σ)

Answer 3

b

b (i.e., the word of length 1 with just symbol b)

Question 4

Regex Notation: r + s

Answer 4

Choice

all words matched by r or by s

Question 5

Regex Notation: r·s

Answer 5

Concatenation

all words obtained by concatenating a word matched by r, and a word matched by s

Question 6

Regex Notation: r*

Answer 6

Kleene star

all words obtained by concatenating any number of words, provided that each one is matched by r