Doubt

Question

What is identity for regular expressions ?

Answer 1

That depends on the operation-

1. For concatenation, its epsilon(ͼ).

eg- aab.ͼ =aab

2.For union, its phi (ϕ).

eg- aab+ϕ =aab

Answer 2

Identity for concatenation(.) is epsilon, and for union(+) is Phi.