Self doubt in Class of language

Question

If L1 is regular and L2 is CFL then L1.L2 ( . => concat) is ?

Comments

It should be CFL

Answer 1

you can use such logic...

EVERY REGULAR IS CFL...

AND CFL ARE CLOSED UNDER CONCETNATION..

so in such question ...go in this way ..

example if its given that its REGULAR....

apply rules of regular and if satisfy ok....if not then EVERY REGULAR IS CFL...

now apply rules of CFL......if fails again..

EVERY CFL IS RECURSIVE...like that you will get answer easily ...

Answer 2

Let L1 = {e} which is regular  {e=epsilon}

Let L2 = {a^b^n | n>0} which is CFL

L2={ab, aabb, aaabbb,......}

now, L1.L2 = {e.ab, e.aabb, e.aaabbb........} = {ab,aabb,aaabbb....} which CFL

Comments

Best explanation