The following language L over A = {a, b}: L = {a mb n a mb n | m > 0 n > 0}. is not context-free. Find an unrestricted (Chomsky type 0) grammar generating it.

Hint: First, a string a mb n#Abamb can be generated (# is a special symbol erased at the end of generation). Then symbols b can be copied one after another to the right end of the string moving the symbol # to the left for each copied symbol b until # reaches symbols a (and is erased).