add container type to table and 0-index the union type definitions

specs/simple-serialize.md

@@ -62,7 +62,7 @@
 * **bitlist**: ordered variable-length collection of `boolean` values, limited to `N` bits
     * notation `Bitlist[N]`
 * **union**: union type containing one of the given subtypes
-    * notation `Union[type_1, type_2, ...]`, e.g. `union[null, uint64]`
+    * notation `Union[type_0, type_1, ...]`, e.g. `union[null, uint64]`
 
 ### Variable-size and fixed-size
 
@@ -78,16 +78,18 @@ For convenience we alias:
 * `null`: `{}`
 
 ### Default values
+Assuming a helper function `default(type)` which returns the default value for `type`, we can recursively define the default value for all types.
 
 | Type | Default Value
 | ---- | ------------- |
 | `uintN` | `0` |
 | `boolean` | `False` |
-| `Vector[type, N]` | `[Default of type] * N]` |
+| `Vector[type, N]` | `[default(type)] * N]` |
 | `Bitvector[boolean, N]` | `[False] * N` |
 | `List[type, N]` | `[]` |
 | `Bitlist[boolean, N]` | `[]` |
-| `Union[type_1, type_2, ...]` | Default of `type_1` |
+| `Union[type_0, type_1, ...]` | `default(type_0)` |
+| `Container` | `[default(element) for element in container]` |
 
 #### `is_zero`