Use of simplify and assume in deriving Equation 1.4-9

>  restart;
>  ubar:=sqrt(8*K*T/(Pi*m)); Eq. 1.4-1
>  lambda:=1/(sqrt(2)*Pi*d^2*n); Eq. 1.4-3
>  mu:=(1/3)*rho*ubar*lambda; Left part of Eq. 1.4-8
>  n:=rho/m; Right part of Eq. 1.4-8
>  simplify(mu); Getting something close to 1.4-9. 
It does not combine the expressions involving m
since it does not know that m is real and positive. 
We can get Maple to do that using assume.
>  ?assume
>  assume(m>0);
>  simplify(mu); This looks almost exactly like eq. 1.4-9.

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