Heterogeneous selection structure for channels This builds a structure of channels that we wish to select over. This is structured in a way such that

Active choice between `P` and `Q`

The HasDual trait defines the dual relationship between protocols. Any valid protocol has a corresponding dual. This trait is sealed and cannot be i

Passive choice (offer) between `P` and `Q`

Enter a recursive environment

Receive `A`, then `P`

Peano numbers: Increment

Send `A`, then `P`

Recurse. N indicates how many layers of the recursive environment we recurse out of.