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Digest d contains (a) the highest seqnos deliverable for each sender and (b) the highest seqnos
seen for each member. (Difference: with 1,2,4,5, the highest seqno seen is 5, whereas the highest
seqno deliverable is 2). The minimum of all highest seqnos deliverable will be taken to send a stability
message, which results in garbage collection of messages lower than the ones in the stability vector. The
maximum of all seqnos will be taken to trigger possible retransmission of last missing seqno (see DESIGN
for details).