Answer :
a). We have proved all the given conditions.
b). It is true that condition 3 holds for all regular languages L1 and L2.
(a) Regular languages L1 and L2 can be suggested as follows:
Let [tex]L_1={0^{(n+1)} | n\geq 0}[/tex]
and
[tex]L_2={1^{(n+1)} | n\geq 0}[/tex]
We have to prove three conditions:1. L1 ⊈ L2:
The given languages L1 and L2 both are regular but L1 does not contain any string that starts with 1.
Therefore, L1 and L2 are distinct.2. L2 L1:
The given languages L1 and L2 both are regular but L2 does not contain any string that starts with 0.
Therefore, L2 and L1 are distinct.3. (L1 ∪ L2)* = L1* ∪ L2*:
For proving this condition, we need to prove two things:
First, we need to prove that (L1 ∪ L2)* ⊆ L1* ∪ L2*.
It is clear that every string in L1* or L2* belongs to (L1 ∪ L2)*.
Thus, we have L1* ⊆ (L1 ∪ L2)* and L2* ⊆ (L1 ∪ L2)*.
Therefore, L1* ∪ L2* ⊆ (L1 ∪ L2)*.
Second, we need to prove that L1* ∪ L2* ⊆ (L1 ∪ L2)*.
Every string that belongs to L1* or L2* also belongs to (L1 ∪ L2)*.
Thus, we have L1* ∪ L2* ⊆ (L1 ∪ L2)*.
Therefore, (L1 ∪ L2)* = L1* ∪ L2*.
Therefore, we have proved all the given conditions.
(b)It is true that condition 3 holds for all regular languages L1 and L2.
This can be proved by using the fact that the union of regular languages is also a regular language and the Kleene star of a regular language is also a regular language.
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