diff --git a/IA_L/dynamics_and_relativity.tex b/IA_L/dynamics_and_relativity.tex
index 9809af8..0f18545 100644
--- a/IA_L/dynamics_and_relativity.tex
+++ b/IA_L/dynamics_and_relativity.tex
@@ -3546,7 +3546,7 @@ \subsubsection*{Particle decay}
 \end{eg}
 
 \subsubsection*{Particle scattering}
-When two particles collide and retain heir identities, the total 4-momentum is conserved:
+When two particles collide and retain their identities, the total 4-momentum is conserved:
 \[
   P_1 + P_2 = P_3 + P_4
 \]