Regular language

Question

let L1 =a*b* and L2 = {ab} L3 = prefix (L1* intersection L2)

where prefix(L) = { u| uv belongs L for any v} find the number of strings in L3????

Answer 1

L1^*  = (a*b*)* = (a + b)*

Now, L3 = L1* intersection L2 = {ab} 

And prefix(L3) = {$\varepsilon$, a, ab}

So, we have 3 strings in L3.

Comments

Right I also got the same.

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thanks