Update HOME_EXAM.md

HOME_EXAM.md

@@ -304,12 +304,9 @@ Other boolean expressions are
 
 ### Let expression
 ```math
-\frac{<v, σ>⇓<\text{let } v:t, σ> ⇓ σ'}{<\text{let } v : t, σ> ⇓ σ[v : t]}
-```
-
-```math
-\frac{<v,σ> ⇓ t <\text{let } v \text{ : } t,σ> ⇓ σ'}{<\text{let } v \text{ : } t, σ> ⇓ σ[v \text{ : } t]}
+\frac{<v, σ> ⇓ t<\text{let } v:t, σ> ⇓ σ'}{<\text{let } v : t, σ> ⇓ σ[v : t]}
 ```
+Declares the variable $`v`$ with type $`t`$ to current scope.
 
 
 ### Assign expression