if you try to do,

```
julia> Base.ImmutableDict(
:a => 1,
:b => 2
)
```

you get,

```
ERROR: MethodError: no method matching Base.ImmutableDict(::Pair{Symbol,Int64}, ::Pair{Symbol,Int64})
Closest candidates are:
Base.ImmutableDict(::Pair{K,V}) where {K, V} at dict.jl:624
Base.ImmutableDict(::Base.ImmutableDict{K,V}, ::Pair) where {K, V} at dict.jl:625
```

how do you construct a multi-key immutable dictionary?