doubt: Closure Property

Question

Let Exchange(L1) : { XwY |  YwX ∈ L1 , X,Y∈  Σ }

Is Exchange(L1) closed or regular?

If yes please give some prove .

Comments

what is 'w'?

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w∈ Σ* , let Σ = {a,b} 

(just  exchange some part from front and end)

Answer 1

Can you define the notion of closed langauge ...