-\setlength{\thinmuskip}{1.5mu} % by default it is equal to 3 mu
-\setlength{\medmuskip}{2mu} % by default it is equal to 4 mu
-\setlength{\thickmuskip}{3.5mu} % by default it is equal to 5 mu
+\newcommand{\setmuskip}[2]{#1=#2\relax}
+\setmuskip{\thinmuskip}{1.5mu} % by default it is equal to 3 mu
+\setmuskip{\medmuskip}{2mu} % by default it is equal to 4 mu
+\setmuskip{\thickmuskip}{3.5mu} % by default it is equal to 5 mu