``` ucm :hide
scratch/main> builtins.merge
```

Some basics:

``` unison :hide
unique type Cat.Dog = Mouse Nat
unique type Rat.Dog = Bird

countCat = cases
  Cat.Dog.Mouse x -> Bird
```

``` ucm
scratch/main> add
```

Now I want to add a constructor.

``` unison :hide
unique type Rat.Dog = Bird | Mouse
```

``` ucm
scratch/main> update
```