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

Tests a case where concrete abilities were appearing multiple times in an
inferred type. This was due to the pre-pass that figures out which abilities
are being matched on. It was just concatenating the ability for each pattern
into a list, and not checking whether there were duplicates.

```unison
structural ability T where
  nat : Nat
  int : Int
  flo : Float

f = cases
  {nat -> k} -> 5
  {int -> k} -> 5
  {flo -> k} -> 5
  {x} -> 5
```