fix small typo

Author: simongravelle

lammps-tutorials.tex

@@ -2284,8 +2284,8 @@ \subsubsection{System preparation}
 lines thanks to the $\&$ character. The second and third lines are used to indicate that the
 simulation contains 1 type of bond and 1 type of angle (both required by the water molecule).
 The parameters for these bond and angle constraints will be given later. The three last
-lines are for memory allocation. The \textit{labelmap} command assings alphanumeric type labels
-to each numeric atom type, bond type and angle type.
+lines are for memory allocation. The \textit{labelmap} command assigns alphanumeric type labels
+to each numeric atom type, bond type, and angle type.
 
 Now, we can add atoms to the system. First, let us create two sub-regions corresponding
 respectively to the two solid walls, and create a larger region from the union of the