Unfortunately, version vectors are not safe in the presenceof Byzantine nodes, as shown in Figure 1. This is because aByzantine node may generate several distinct updates withthe same sequence number, and send them to different nodes(this failure mode is known as equivocation). Subsequently,when correct nodes p and q exchange version vectors, theymay believe that they have delivered the same set of updatesbecause their version vectors are identical, even though theyhave in fact delivered different updates.

Comparing version vectors betweenpayloads is an inclusion check without the need to perform aDAG-walking