Add series navigation before appendix

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

content/blog/02_spa_agda_combining_lattices.md

@@ -449,6 +449,8 @@ The same is true for maps, under certain conditions.
 The finite-height property is crucial to lattice-based static program analysis;
 we'll talk about it in more detail in the next post of this series.
 
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 ### Appendix: Proof of Uniqueness of Keys
 
 I will provide sketches of the proofs here, and omit the implementations