error[E0308]: `case` clauses have incompatible types
   ┌─ FizzBuzz.fun:16:16
   │  
10 │   fizz₂ : Nat → String
   │                 ------ expected type `String` found here
11 │   fizz₂ num =
12 │ ╭     case (mod num 5) (mod num 3) of
13 │ │         0 0 => "FizzBuzz"
   │ │                ---------- this is found to be of type `String`
14 │ │         0 _ => "Fizz"
   │ │                ------ this is found to be of type `String`
15 │ │         _ 0 => "Buzz"
   │ │                ------ this is found to be of type `String`
16 │ │         _ _ => num
   │ │                ^^^ expected `String`, found `Nat`
   │ ╰──────────────────' `case` clauses have incompatible types
   │  
   = expected type `String`
        found type `Nat`