fix mathematics

docs/source/reference/kernelcreation.md

@@ -450,6 +450,15 @@ We use the integer remainder ({any}`int_rem`) to distinguish between even- and o
 set the start value accordingly using {any}`sp.Piecewise <sympy.functions.elementary.piecewise.Piecewise>`,
 and use a step size of two:
 
+$$
+  start(y)=
+    \begin{cases}
+      0 & \quad \text{if } y \% 2 = 0 \\ 
+      1 & \quad \text{otherwise}
+    \end{cases}
+$$
+
+
 ```{code-cell} ipython3
 from pystencils.sympyextensions.integer_functions import int_rem