I have the the following expression:
$ tan(m \cdot actan(x) + n \cdot arctan(y))$
For what values of $n,m \in \mathbb{N}$ is this expression reducible to a rational expression in $R[x,y], where R is generic ring$?
Is there some rule $lhs => rhs $ that is needed in order to get a rational expression form the expression above?