"example_rexps":- ::= $ | a+ -- = a*, zero or more as ::= aa* -- = a+, one or more as ::= $ | a -- = a?, zero or one as ::= a{3} -- = aaa, three as ::= a{3,5} -- = a{3}a?a? ::= a{3,} -- = a{3}a* "example_sets":- ::= a-z -- little letters ::= ~a-z -- anything but little letters ::= [a-zA-Z0-9] -- letters and digits ::= `!@@#$' -- the symbols !, @@, # and $ ::= [`!#@@$'^'^n] -- the above symbols with ' and newline ::= ^p#^' -- any graphic character except ' ::= ^127 -- ASCII DEL