Describe the language denoted by the following regular expressions:
a) a(a|b)*a
The expression denotes the set of all strings of length two or more that start and end with an ‘a’.
b) ((e|a)b*)*
The expression denotes the set of all strings over the alphabet {a,b}.
c) (a|b)*a(a|b)(a|b)
The expression denotes the set of all strings of length 3 or more with an ‘a’ in the third position from the right. Ie of form yaxz where y is an arbitrary string , and x and z are single characters.
d) a*ba*ba*ba*
The expression denotes the set of all strings that contain precisely 3 b’s.
e) (aa|bb)*((ab|ba)(aa|bb)*(ab|ba)(aa|bb)*)*
The expression denotes the set of all strings of even length.
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