kill(all);

assume(a>0,b>0,c>0);

f(a,b,c):=(%e^(a^5-a^3+1)+%e^(b^5-b^3+1)+%e^(c^5-c^3+1))/(3*%e);

g(a,b,c):=2*(a*b*c)^(1/3)-1;

f(x,y,z);

subst(MathdE,%e,f(x,y,z));

g(x,y,z);

f(x,y,z)-g(x,y,z);

subst(e,%e,%);