diff --git a/pdf/grandpa.tex b/pdf/grandpa.tex index 31c84ae..9dc00a3 100644 --- a/pdf/grandpa.tex +++ b/pdf/grandpa.tex @@ -38,7 +38,7 @@ Each round has two phases, each of which has an associated vote, prevote and pre For block $B$, we write $\mathrm{chain}(B)$ for the chain whose head is $B$. The block number, $n(B)$ of a block $B$ is the length of $\mathrm{chain}(B)$. For blocks $B'$, $B$, $B$ is later than $B'$ if it has a higher block number. -We write $B > B'$ or that $B$ is descendant of $B'$ for $B$, $B'$ appearing in the same blockchain with $B'$ later i.e. $B \in \mathrm{chain}(B')$ with $n(B') > n(B)$ and $B < B'$ or $B$ is an ancestor of $B'$ for $B' \in \mathrm{chain}(B)$ with $n(B) > n(B')$ . $B \geq B'$ an $B \leq B'$ are similar except allowing $B = B$. We write $B \sim B'$ or $B$ and $B'$ are on the same chain if $B B'$ and $B \nsim B'$ or $B$ and $B'$ are not on the same chain if there is no such chain. +We write $B > B'$ or that $B$ is descendant of $B'$ for $B$, $B'$ appearing in the same blockchain with $B'$ later i.e. $B \in \mathrm{chain}(B')$ with $n(B') > n(B)$ and $B < B'$ or $B$ is an ancestor of $B'$ for $B' \in \mathrm{chain}(B)$ with $n(B) > n(B')$. $B \geq B'$ and $B \leq B'$ are similar except allowing $B = B$. We write $B \sim B'$ or $B$ and $B'$ are on the same chain if $B B'$ and $B \nsim B'$ or $B$ and $B'$ are not on the same chain if there is no such chain. Blocks are ordered as a tree with the genesis block as root. So any two blocks have a common ancestor but two blocks not on the same chain do not have a common descendant. @@ -73,7 +73,7 @@ Note that it is possible for an intolerant $S$ to both have a supermajority for \begin{lemma} \label{lem:impossible} \begin{itemize} \item[(i)] If $B' \geq B$ and it is impossible for $S$ to have a supermajority for $B$, then it is impossible for $S$ to have a supermajority for $B'$. -\item[(ii)] If $S \subseteq T$ and it is impossible for $S$ to have a supermajority for $B$ +\item[(ii)] If $S \subseteq T$ and it is impossible for $S$ to have a supermajority for $B$, then it is impossible for T$ to have a supermajority for $B$. \item[(iii)] If $g(S)$ exists and $B \nsim g(S)$ then it is impossible for $S$ to have a supermajority for $B$. \end{itemize} \end{lemma} @@ -351,4 +351,4 @@ We only need the primary for liveness. We need some form of coordination to defe When the network is well-behaved, an honest primary can defeat this attack by deciding how much we should agree on. We could also use a common coin for the same thing, where people would prevote for either the best chain containing $E_{r-1,v}$ or $g(V_{r-1,v})$ depending on the common coin. With on-chain voting, it is possible that we could use probabilistic finality of the block production mechanism - that if we don't finalise a block and always build on the best chain containing the last finalised block then not only will the best chain eventually converge, but if a block is behind the head of the best chain, then with positive probability, it will eventually be in the best chain everyone sees. In our setup, having a primary is the simplest option for this. -\end{document} \ No newline at end of file +\end{document}