kill(all);

van=facebook.com/LearningCalculus$

f(x,y):=x^4/(x^3+y^3);

limit(limit(f(x,y),x,0),y,0);

fpppX(x,y):= ''(diff(x^4,x,3));

gpppX(x,y):= ''(diff(x^3+y^3,x,3));

limit(fpppX(x,y)/gpppX(x,y),x,0);

limit(%,y,0);