# automata – Write the Context free Grammar

What will be the context-free grammar of $$B= A_1.A_2$$
when $$A_1 = {0^n1^n|ngeq 0}$$
$$A_2 = {1^n0^n|n geq 0}$$
Also verify using a string.

if the Grammar for
$$A_1$$: $$S_1 rightarrow 0S_11 | varepsilon$$

$$A_2$$: $$S_2 rightarrow 1S_20 | varepsilon$$

I am stuck with the value of $$S rightarrow$$ ?