How do you say "if and only if" in Japanese?

Question

I would like to know how to express mandatory conditions in Japanese. Since Japanese distinguishes between different types of languages, I should probably ask more precisely: What is the right way to express equivalence statements (the kind a mathematician might make) such as "The equation is satisfied if and only if a>b"? How do you express that you're going to do or that something will happen, only if some condition is satisfied? ("I'll only go if you buy me an ice.", "The plant will only grow if it is watered regularly.")

Answer 1

I think the ば conditional would work best.

アイスを買ってくれば行く。

水をやれば植物が伸びる。