Write a new post about proving the connection between semantics and CFGs

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

content/blog/06_spa_agda_cfg/index.md

@@ -190,6 +190,7 @@ some of the indices of the elements within. For instance, in the lists
 concatenated list `[x, y]`, the index of `x` is still `0`, but the index of `y`
 is `1`. More generally, when we concatenate two lists `l1` and `l2`, the indices
 into `l1` remain unchanged, whereas the indices `l2` are shifted by `length l1`.
+{#fin-reindexing}
 
 Actually, that's not all there is to it. The _values_ of the indices into
 the left list don't change, but their types do! They start as `Fin (length l1)`,