= Lazy feedback stream
Mutually dependent streams evaluated by <lazy evaluation>. A useful sufficient condition for <productivity> is that one participant emits its first constructor independently of any reply, while its $(j+1)$-st output depends only on the first $j$ replies. A scorer mapping each guess to a terminating response then lets each finite interaction prefix be constructed inductively. Inspecting the reply stream before emitting the first guess instead creates a circular demand.
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