Difference between ∑ and ∑1

Question

I learn a deterministic final automat, nondeterministic,regex... And I found that is important to know a difference between ∑ and ∑1 since they both the same if ∑={0,1}, but I will answer that ∑1 is result of concatenation epsilon and 0,and the epsilon and 1.How would you answer that the question is asked by the professor?

Answer 1

• Well, sigma is a finite set of input symbols called the alphabet ∑.

• ∑1 on the other hand is the word w consisting of one letter of the alphabet ∑, hence the 1 in ∑.