diff --git a/300s School/ME 2016 - Nonlinear Dynamical Systems 1/2024-09-30 Limit Cycles.md b/300s School/ME 2016 - Nonlinear Dynamical Systems 1/2024-09-30 Limit Cycles.md
index b18ff032..b96d7fbe 100644
--- a/300s School/ME 2016 - Nonlinear Dynamical Systems 1/2024-09-30 Limit Cycles.md	
+++ b/300s School/ME 2016 - Nonlinear Dynamical Systems 1/2024-09-30 Limit Cycles.md	
@@ -57,3 +57,6 @@ $= 2 c_1 x(y-x^3) + 2c_2 y(-x-y^3)$
 Assume $c_1 = c_2$
 ... $\therefore \frac{dV}{dt} = -2c(x^4+y^4) < 0$
 Therefore limit cycles are not possible. 
+
+### Index Method
+This is a method covered in the book. Sometimes is used to rule out limit cycles.