I was solving some problem from past test, there was this question:
Use the closure property of regular language to show the language $L$ is not regular
$$L =\{ a^3 b^n c^{n-3} \mid n>3\} $$
I know how to solve it using Pumping Lemma, but how to solve it with closure property?
Also, I know that to prove that a language L is not regular using closure properties, the technique is to combine L with regular languages by operations that preserve regularity in order to obtain a language known to be not regular, but I can't figure out with whom to combine.
I saw some similar questions but didn't get ideas about how to do this one.
Any hints?
Thanks.