Write up the "verified" portion of the forward analysis

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

content/blog/05_spa_agda_semantics/index.md

@@ -262,6 +262,7 @@ expressions, and the letter \(v\) to stand for values. Finally, we'll write
 \(\rho, e \Downarrow v\) to say that "in an environment \(\rho\), expression \(e\)
 evaluates to value \(v\)". Our two previous examples of evaluating `x+1` can
 thus be written as follows:
+{#notation-for-environments}
 
 {{< latex >}}
 \{ \texttt{x} \mapsto 42 \}, \texttt{x}+1 \Downarrow 43 \\