LHS
(a (ba)* (a + bb) + b (ab)* (b + aa)) (a+b)*
Initially we have two choices,
a (ba)* (a + bb) : In this expression, at minimum either aa will accept or abb will accept.
b (ab)* (b + aa) : In this expression, at minimum either bb or baa will accept.
observe both, it says either aa or bb will accept.
When we done with choices, we will accept everything i.e (a+b)*
So it says at minimum we have to see either aa or bb, then we dont care what comes after that, we will accept everything.
RHS
(a+b)* (aa+bb) (a+b)* : It says that we will not accept the string until we see aa or bb as substring. Which is same as what RE at LHS says.
