Regular Expression Examples

a = {a}

ab = {ab}

a | b = {a, b}

a+ = {a, aa, aaa, ... }

ab* represents the set of strings having a single a followed by zero or more occurrences of b.

That is, it’s {a, ab, abb, abbb, ... }

a (b | c) = {ab, ac}

(a | b) (c | d) = {ac, ad, bc, bd}

aa* = a+ = {a, aa, aaa, ... }