Update L17 slides for math error in count function, slide 18

Lectures/L17_MathReviewPlusExample/MathReviewPlusExample.tex

@@ -357,7 +357,7 @@ $\forall (a: \mathbb{R} | a \in A : \exists(b: \mathbb{R} | b \in B: b = a)
 \wedge \mbox{count}(a, A) = \mbox{count}(b, B)) \wedge \forall (i: \mathbb{N} | i \in [1..|A|-1] : B_i \leq B_{i+1})$\newline
 
 \noindent $\mbox{count}(a, A): \mathbb{R} \times \mathbb{R}^n \rightarrow \mathbb{N}$\newline
-$\mbox{count}(a, A): + (x: \mathbb{R} | x \in A \wedge x = a : 1)$\newline
+$\mbox{count}(a, A) \equiv + (x: \mathbb{R} | x \in A \wedge x = a : 1)$\newline
 
 \noindent $\mbox{avg}(C): \mbox{ set of } \mathbb{N} \rightarrow \mathbb{R}$\newline
 $\mbox{avg}(C) \equiv + (x: \mathbb{N} | x \in C : x) / |C|$\newline