# When proving an iff (<==>), is there a nice way to prove this by proving each side of the implication separately without making 2 different lemmas?

### Question

When proving an iff (<==>), is there a nice way to prove this by proving each side of the implication separately without making 2 different lemmas?

### Answer

Here are two ways to prove `A <==> B`

:

```
if A {
// prove B...
}
if B {
// prove A...
}
```

Another way is

```
calc {
A;
==
// ...
==
B;
}
```