Suppose, A = { 0^n | n > 0 } and
B = { 1^n | n > 0 }
By def. of a and b having any no of 0s and 1s repectively
both are regular languages
BUT, A ∘ B = { 0^n.1^n | n >0 }
which is a renowned cfl .
same applies for → B∘A
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