My book says that $f(x,y,z) = xy + yz + zx$ is self dual function but $(x+y)(y+z)(z+x)$ is not.
I understood how $xy + yz + zx$ is self dual but I think $(x+y)(y+z)(z+x)$ is also self dual because in k-map if we represent $(x+y)(y+z)(z+x)$ then it's minimized SOP is $xy + yz + zx$ and if we take dual of this, then we get original $(x+y)(y+z)(z+x)$. I think self dual is commutative.
Am I correct?