"Express the fact that b and c are the same size if and only if one is a tetrahedron and the other is a dodecahedron.

"Express the fact that b and c are the same size if and only if one is a tetrahedron and the other is a dodecahedron." I have tried many different ways, such as "SameSize(b,c) ↔ (Tet(b) ∧ Dodec(c)) ∨ (Tet(c) ∧ Dodec(b))" and none of them are right. I am not sure what else to try as what I have put seems like it should be correct.