Symmetric: For binary structures $$S$1,$ and $$S$2,,$ if S$1\text{'}$ S$2$

then S$2\text{'}$ S$1.$ Hint: assume $\backslash$phi : S$1->$ S$2$ is an isomorphism and

prove that $\backslash$phi $1$ : S$2->$ S$1$ is also an isomorphism.