My textbook has a problem to find the regular expression that describes the set of all strings of
1's whose number of
0's is divisible by
5 and whose number of
1's is even.
I can write a regular expression for each condition
I am having trouble understanding how to combine these two regular expressions. If they were DFAs, I could combine them by taking their cartesian product. Is is possible to take the cartesian product of two regular expressions (without translating each to a DFA first)?