I saw this question in a textbook on decidable languages, and I was wondering how you would go about solving this type of question:
Assume L1 and L2 are decidable languages. Which of the following are decidable?
a. L1 Union L2
b. L1 Intersection L2
c. L1 - L2
I know that a decidable language is one that does not create a loop in a Turing machine and that it is Turing machine recognized, but I am not sure how to go about solving for these.
All I can think of, is that if a turing machine can decide L1 and L2, then a and b should be decidable but not c. Am I right or wrong?
Any explanation helps, thanks.