I need to show that if A and B are isomorphic, then A and B are elementarily equivalent with a proof by induction on formulas.

A and B are first-order structures for a first-order language, L.

A and B are isomorphic if there is a bijection h: domain of A -> domain of B such that

h(c^A)=c^B

h(f^A(a1,...,an))=f^B(a1),...,f^B(an)

(a1,...,an) contained in P^A iff (h(a1),...,h(an)) contained in P^B.

I also am given that

Th(A)={psi l A l= psi}

A is logically equivalent to B iff Th(A) =Th(B)

*where Th(A) means the theory of A