Converting to regular expressions I am really not sure about the following problem, I tried to answer it according to conversion rules the best I can. I was wondering if someone can give me some hints as to whether or not I am on the right track.
Many thanks in advance.
Convert to Regular Expressions
L1 = {w | w begins with a 1 and ends with a 0.}  = 1E*0
L2 = {w | w contains the substring 0101} = E*0101E*
L3 = {w | the length of w does not exceed 5} = EEEEE
L4 = {w | every odd position of w is a 1} = (E*=1 intersection E*E*)
L5 = { w | w contains an odd number of 1s, or exactly 2 0s. } = (E)* U (E=0)*2

$L3$ is wrong, what you give is all of length exactly 5.
$L4$ should be something like $(1E)^*(1|\epsilon)$
$L5$ is the union of two branches: Odd number of 1, exactly 2 0. Left as an exercise to the reader ;-)
