quantities in case don't need to be *exactly* the same

...as long as they are all compatible with the target.
for example, given ω.n : ℕ:
```
  case double_it? return ℕ of {
    'true  ⇒ plus n n;
    'false ⇒ n
  }
```

lib/Quox/Syntax/Qty/Three.idr

@@ -50,6 +50,13 @@ times One  rh   = rh
 times pi   One  = pi
 times Any  Any  = Any
 
+public export
+lub3 : Three -> Three -> Maybe Three
+lub3 p q =
+  if p == Any || q == Any then Just Any
+  else if p == q then Just p
+  else Nothing
+
 public export
 data Compat3 : Rel Three where
   CmpRefl : Compat3 rh rh
@@ -103,6 +110,8 @@ IsQty Three where
   (+) = plus
   (*) = times
 
+  lub = lub3
+
   IsZero     = Equal Zero
   isZero     = decEq Zero
   zeroIsZero = Refl