Fix markdown

book/src/fork-deltas.md

@@ -16,7 +16,8 @@ The basic design idea is to maintain a DAG of forks.  Each fork points back to a
 An *active fork* is a direct list of connected forks that descend from the current root to a specific fork without any descendants.
 
 For example:
-```
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+```art
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@@ -41,7 +42,7 @@ A validator votes for a finalized fork.  The *active fork* connecting the fork t
 
 For example:
 
-```
+```art
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@@ -55,7 +56,7 @@ For example:
 
 * ROLLBACK\_DEPTH=2, vote=5, *active fork*={5,2,1}
 
-```
+```art
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@@ -67,7 +68,7 @@ The new root is 2, and any active forks that are not descendants from 2 are prun
 
 * ROLLBACK\_DEPTH=2, vote=6, *active fork*={6,1}
 
-```
+```art
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     2   \