I was trying to do the following:
Consider the set of all strings over the alphabet {0,1,2,9} that are decimal numbers beginning with 1 and ending with 9 and having exactly one decimal point (.). For example 12.9, would be a valid decimal number while 0.129 would be not since it does not begin with 1.
but it didn't seem to work:
1(0|1|2|9)*.(0|1|2|9)*9
or
S::=1X
X::=E|0X|1X|2X|9X|Y
Y::=.Z
Z::=E|0Z|1Z|2Z|9Z|A
A::=9
Why? Whats the correct answer?