## 19.4 The tactic itself

After having registered all the setoids and morphisms you need, you can use the tactic called `Setoid_replace`. The syntax is

> `Setoid_replace` term1 with term2

The effect is similar to the one of `Replace`.
You also have a tactic called `Setoid_rewrite` which is the equivalent of `Rewrite` for setoids. The syntax is

> `Setoid_rewrite` term

Variants:

1. `Setoid_rewrite ->` term
2. `Setoid_rewrite <-` term

The arrow tells the systems in which direction the rewriting has to be done. Moreover, you can use `Rewrite` for setoid rewriting. In that case the system will check if the term you give is an equality or a setoid equivalence and do the appropriate work.