Across a network, there is a possibility that two different
blocks are added at the same time by different nodes,
creating a fork in the chain. In this case, there is a ‘consensus
rule’ that helps nodes figure out which is the block they
should believe. In bitcoin, the rule is called the ‘longest
chain rule’ – each node acknowledges the legitimacy of
both contender blocks and the situation resolves when the
next block is built on one of the contenders. The longer
chain becomes part of the de-facto blockchain


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