Concurrent Sends to 1 Stream

with this approach:

declare L0                  %% L0 = _
declare L1 in L0=a|L1       %% L0 = a|_
declare L2 in L1=b|L2       %% L0 = a|b|_
declare L3 in L2=c|L3       %% L0 = a|b|c|_

we cannot have more than 1 agent appending messages to the same stream

a new abstraction is needed to mediate the operation of extending the stream with a new message