Basic Regular Expressions in Lex
[0-9]
0 + 1 + 2 + …+ 9
[a-z]
a + b + c + …+ z
r?
r + e
r+
r+
r*
r*
r|s
r + s
rs
r.s
a
a
RE in LEX
Equivalent RE in theory of formal languages
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