- Fixed the fixpoint combinator semantics and type
- Introduced labelled transitions and labels for computation
placeholders
- Now the double computation fork death reduces based on the select
operator (they could be in two orders we may not pick one as that would
break commutativity). Note how there is a specificity order of reduction
for this case, so that we end up returning { unit, unit } rather than
{unit, live exp unit } though this seems not mandatory.